Putting cable for solar through the roof. - Fiberglass RV
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Old 06-30-2020, 09:56 AM   #1
Junior Member
Name: Greg
Trailer: bigfoot
Posts: 12
Putting cable for solar through the roof.

I'm planning to mount a 100w solar panel on my B17 Bigfoot that I am restoring. I'm wondering how the hole through the roof should be made secure and waterproofed. Should some kind of plastic conduit be placed in the hole first and then sealant applied after putting the wire is through?

For the location of the panel I'm thinking putting it near the front of the trailer. Would this be okay or is there a better spot? The ceiling is out on the interior to run the wires so I could place it anywhere.

I guess I'll screw the panel down as well since I can put wooden braces on the inside to secure to but it is tempting to use 3M VHB tape - thoughts? It has been a challenge to get the roof reinforced and waterproofed so I'm hesitating before putting holes in it!
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Old 06-30-2020, 10:35 AM   #2
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Name: Tom
Trailer: BigFoot 25B25RT
Posts: 446
What do you have for existing holes on the roof. TV antenna, refrigerator vent or something similar could be used rather than making another hole.
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Old 06-30-2020, 11:35 AM   #3
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Name: Greg
Trailer: bigfoot
Posts: 12
The only things in the roof right now are the Fan-tastic Fan and the bathroom vent.
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Old 06-30-2020, 01:24 PM   #4
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Name: Christian
Trailer: Scamp 13'
Posts: 27
I installed a flexible panel on my 13' Scamp. I used this double cable gland to route the cables through the roof. The wires enter inside an upper cabinet. I used conventional raceway to manage the vertical run to the solar charger. The cable gland yellowed nearly instantly but isn't brittle.

I also used VHB to secure my panel, although I did add 3 rivets on the front edge (just in case) and laid clear Gorilla Tape over that as well to prevent water ingress.
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Old 06-30-2020, 01:34 PM   #5
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Name: Nicolas
Trailer: 1978 Boler
Almonte, Ontario
Posts: 122
For the cable pass-through, i would recommend a rubber wire grommet that auto parts stores sell. They are meant to go into holes drilled into the body of the car and sit around the hole so that, if installed with a bead of butyl caulk will seal really well and if the grommet is sized to your cable, a bead of butyl on the cable just as it is seated should seal that too.

As for fastening the solar panels, i would suggest attaching studs to the roof to mount the panels/panel frame to. What you need to do is decide where the studs need to be placed; sand/grind down to expose the fibreglass; fibreglass those cute bolts with flat heads that are used to slide in tracks like a table saw; layer successive layers of fibreglass cloth to form a secure base; sand to make it look good and no one will ever know that you didnít drill through the shell.
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Old 06-30-2020, 01:52 PM   #6
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Name: Gordon
Trailer: 2015 Scamp (16 Std Layout 4) with '15 Toyota Sienna LE Tug
North Carolina
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Old 06-30-2020, 02:30 PM   #7
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Name: Z
Trailer: Sasquatch
Posts: 2,550
I have the linked cable entry plate. Some would say it's overkill and they're likely right, but it seemed like the right tool for the job. It's expensive. I'm very inexperienced but keep in mind that, so far as I can tell, it's not meant to be used to simply run long cables through, from the roof to the controller. The plate is meant to have MC4 connectors mounted in it, so you'd need to cut the wire and attach those. If you buy the plate with these already mounted with attached wire long enough to make it to the charge controller...even more expensive. Seems to be hard to track down lately, too.

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I went with just VHB tape for my panel but if I had to do it again, I'd probably at least bolt two diagonal corners, through the ceiling. I likely will do that at some point. You'll hear from people from both camps, but in the end, there are already holes in your roof. So long as you seal them, they won't leak. I used VHB tape, covered with sealant (sikaflex, which was a mistake), covered again with eternabond tape, which adds more stability/larger footprint of adhesion. But still...crazy enough gust of wind driving at highway speeds...

I put my panel on the back end of the roof, ran the wires along the roof to the front, driver side corner, closest to the power center and battery, then down through that corner into the cabinets, along the corner beam, down into the lower cabinets/dinette, to the charge controller which I mounted under the front dinette seat, right above where all the wires come through the floor. Close to the battery.


You have the benefit of a torn-apart trailer to work with. You can add supports and anchors anywhere you want for securing things.
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Old 06-30-2020, 05:34 PM   #8
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Name: Greg
Trailer: bigfoot
Posts: 12
Good advice. Thanks everyone.
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Old 07-01-2020, 12:28 PM   #9
Name: Thomas
Trailer: Casita Independence 17í
Posts: 35
Solar wires thru roof

Please check out Slim Potato Head on YouTube. he just did a solar panel install on his Outback 13' trailer.

Tom C
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Old 07-02-2020, 06:36 AM   #10
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Name: Gilles
Trailer: Bigfoot 25B21RB, 2004
Posts: 693
According to the year and the model there are different possibilities for the passage of the wiring, without making perforations.
What are yours?

Model : 15B17G, 15B17**, 25B17**, ??
Year ?
Shower or not ?

Have a good day.
Bigfoot 25B21RB.
Towed with Dodge RAM 1500 Echo-Diesel, 3.0 L., 8 speeds.
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Old 07-02-2020, 09:10 AM   #11
Name: Cate & Dan
Trailer: 1976 Triple E SurfSide "The Mutt Hut"
Posts: 56
If you look at page 4 0f Rookie vs. 1990 Casita, he uses a flexible conduit to run his wiring for his harness. I thought this was a nifty idea and picked up one to do the same on our trailer reno. Perhaps this would work for your solar. They are available at Lowes, HD etc. Just a suggestion.
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Old 07-08-2020, 11:32 AM   #12
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Name: Mike
Trailer: 1977 Scamp 13'
Posts: 20

I mounted my Renogy 100W solar panel on the roof using 3M VHB tape - it's been there for over 5 years and is still solid. It's not coming off!

To run the wires into the trailer, I used Newmar RA-1 cable feed-thru's. These are designed for use on sailboats, and are bomb-proof. They're completely water-tight, and they don't break down under UV light. On my Scamp, I mounted the feed-thru's on the roof over the cupboard. My charge controller is mounted inside the cupboard.
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Old 07-08-2020, 11:48 AM   #13
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Name: Danny
Trailer: 2017 R Pod 179
Posts: 7
If you don’t already have a convenient hole in your roof, drill a hole in the bathroom vent pipe and another, in the same pipe, just above the roof.

Pass the cable through the vent pipe and then silicone the two holes.

No need for drilling in the roof.
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Old 07-08-2020, 12:01 PM   #14
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Name: Tony
Trailer: Boler
Posts: 119
Have not read the responses you have buuut here is what I did on the Burro,
went down the sewer vent pipe, which passes through the back of the fridge bay. In our case there happened to be a T with a plug in the sewer pipe, so just fished the wire out and drilled a hole in the plug for the wire, used rtv to seal it up.
On our Toyota Sunrader, I went into the vent which had wiring for an airconditioner, so connected to that then at the 120V breaker panel disconnected the wire and connected them to a solar controller then the batteries, On our coach, went in through the roof vent for the fridge, straight down to the basement locker controller & batteries. In 1998, Back when solar controllers cost almost as much as panels, came down through the fridge roof vent and just connected to the fridge circuit with no controller, since we were full timing our usage exceeded any solar input so no worries.
We're lost but we're making good time.
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Old 07-09-2020, 09:14 AM   #15
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Name: Kelly
Trailer: Trillium Outback 13'
Posts: 4
Originally Posted by Thomas A Cronquist View Post
Please check out Slim Potato Head on YouTube. he just did a solar panel install on his Outback 13' trailer.
Tom that's a great video and I never would have found it otherwise. Thanks for posting it, I have the exact same trailer and want to put a similarly huge solar panel on mine.

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Old 07-09-2020, 10:19 AM   #16
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Trailer: Sasquatch
Posts: 2,550
People will go back & forth on the VHB tape. In the end, it's only a matter of time and the right gust from a passing semi. I agree the bond is strong. The bond is not going to break. But the actual attachment is only as good as the layer you attach it to. Escape stopped selling trailers with only VHB tape solar installs, because when they started coming off trailers, it was because they pulled a layer of gelcoat and fiberglass off with them.

I saw it on my roof when I needed to remove my first cable hatch install. I was "chipping" the tape off the roof, I when I pulled one spot up, a piece of my roof came up with it.

You may well use VHB tape and never have a problem. It's a matter of the right air gust hitting at the right angle.
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