need to build a floor for my fiberglass cargo van - Fiberglass RV

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Old 07-31-2013, 02:56 PM   #1
Junior Member
Name: Noah
Trailer: Unicell Van Body
Posts: 1
need to build a floor for my fiberglass cargo van

So, I have a Ford Econoline with an aftermarket fiberglass body that I want to turn into a camper. I want it to be fully insulated. The first thing I have to do is put a floor in. It used to have a 3/4" plywood floor that sat right on top of the metal frame of the van. I tore it out because it was filthy, rotting in places, damp, etc. I'm glad I did because the frame was very rusty, and need to be reinforced in key areas.

I don't really know what I'm doing. I'm especially ignorant when it comes to floor theory. My thinking is that I need a moisture barrier between outside and the insulation in the floor, and another moisture barrier between the living space and the insulation.

So, what I was thinking was a base plywood layer, then some sort of plastic tarp on top of it, which I'd tape to the sides of the van using some sort of heavy-duty extremely sticky tape, in order to create a seal. On top of that layer, I'd lay 2x4's with the spaces between them filled with rigid foam sheets. I'd put another tarp over that, then plywood over that, which would be my actual floor.

Would I need to vent anything? Would I need to treat that base plywood layer with anything, or just paint it? It would be exposed to the road. The only thing that would actually be fixed to the sides of the van would be the taped tarp. I'd wedge the foam in really tight to guard against air flow. Is that enough?

Here's a picture of the inside of the van:

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Old 08-01-2013, 03:26 PM   #2
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Name: Brian
Trailer: Boler (B1700RGH) 1979
Posts: 5,000
Hi, Noah. Although this is a trailer forum, the Unicell van bodies come up in discussion occasionally (example: What is this??) because the look interesting (the Aerocell SRW anyway) and are moulded fiberglass. Do you have the big hatch rear door?

I understand the floor sandwich plan, but if suitably strong extruded polystyrene foam is used as this insulation (such as the right Styrofoam product from the wide range), and the layers are glued together, the 2x4s are not required. Many RV floors (but not typically the floors of our moulded fiberglass travel trailers) are built this way. A sheet of this foam wouldn't need a moisture barrier under it. With the whole sandwich adding strength, the top layer should not need to be as thick as the 3/4" original.

1979 Boler B1700RGH, pulled by 2004 Toyota Sienna LE 2WD
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Old 08-02-2013, 07:28 AM   #3
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Trailer: 84 16 ft Scamp
Posts: 725
The fellow who bought our 26 ft Avion last fall which we hadn't used for over 15 yrs found some softness in the bathroom and kitchen. Since the original ply-foam laminate was of odd thickness he decided to replace the entire floor.

Since this trailer was built before the gray water laws, I had made the newly gray conversion about 30 yers ago. My tank I built of 3/8 marine ply with a bladder of 3 mil black poly sheeting of the Visqueen brand. Before installing the bladder I added 3\8 ply doubling strips from scrap around top and bottom for strength, then gave the entire box several coats of Verithane polyurethern varnish that was available at that time. For the bladder I folded the corners of the poly sheeting nicely and glued (with GE silicone) and stapled the poly to the doubled top of the box, as it was at that point and trimmed the edges.

The bottom of the top was likewise glued with marine grade silicone stapled around the edges. When partially set up, the top was g;ued and screwed to the box using stainless wood screws.

I go through this because after more than 30 years this tank was still in great shape. The new owner pulled the tank, tested it by filling it with water, added a 6-inch access at a logical place in the top for future flushing and cleaning, sanded the exterior, filled some gouges on the bottom and gave a new coat of polyurethane exterior varnish. We were both amazed how well that tank had performed over the many roads and years!

So the new owner, the biggest Asian Vietmese fellow I've ever known, and an excellent craftsman was happy to invest in marine grade ply for the new floor. After cleaning the frame, replacing some rusty parts (he's really accomplished with a small wire-feed welder) he PUR-15'd the entire frame, then coated it with several of black poly.

The new floor is a ply/expanded poly/ply sandwich as close in thickness as the original as he could make, but made with better materials and better construction practices than original. His wife, a beautiful Samoan, very proficient with a sewing machine as well as a table saw, redid the curtains and modified the twin aisle beds and front couch/bed appropriate for new futon mattresses all in a southwest Asian Polynesian motiff.

Unfortunately I was having severe health problems when they brought it by to show us. They are temporarily working in North Dakota and use it to supplement their small apartment. They also pull it with an upgraded vintage Ford pickup of the same year model, 1970.

So with the better materials available today any project like this is only constrained by your imagination and abilities. Good luck.
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