Correct sealant for soft rubber tail light

[Joe & Cherie]

Hi all,

I hope everyone is staying safe out there! Please be safe but try to enjoy some normalcy as well!

Hey I’m looking for a little help! My tail light started to let a little water in on hard rains. A hose test confirmed it was the tail light!

Here’s the deal. It’s a soft rubber seal that presses into the hole in the fiberglass, then the hard light presses into the soft rubber seal.

So upon removal, there is nothing between the hard light and the soft seal. Just the presses fit makes the seal. But there was white caulking between the fiberglass and the rubber seal.

So upon redoing it, what would you use? Should I use dicor to seal the soft rubber ring to the fiberglass? Then nothing between the light and rubber? Or silicone between the plastic light and rubber ring? But mainly I’m looking for best sealant to seal rubber ring to the fiberglass!


2013 EggCamper
Thank you!

[Donna D.]

I'd use butyl.

[Joe & Cherie]

Donna I thought that too because I used it on windows and vents etc, and I agree silicone should not be on fiberglass. But this black rubber ring is very very soft and squishy! It’s almost like the butyl tape would not allow the rubber to even press against the fiberglass. I do realize the setup is different than most! If it were a hard ring, I’d use butyl for sure!

[Donna D.]

Then perhaps ProFlex or Sikaflex 221.

[Joe & Cherie]

Awesome! I’ll look into those! I hope Lowe’s has em! Thanks for the tips, I was so unsure on this one. Gotta admit I don’t like the setup. Rather have hard external lights but I already have the big hole so I can’t change em lol.

[mary and bob]

I have bought Proflex at Amazon or a RV dealer. I don't think Lowes or Home Depot has it. But they may have a gutter seal product in a tube that is butyl. Proflex comes in a caulk gun tube, clear or white that I know of.

[C&G in FL]

IMHO, I would not use Proflex with something soft and squishy. If you ever need to remove it, it will be destroyed as once dry, Proflex is like a strong glue and the piece will only come out in chunks and pieces. What is the sealant currently on it? Is it hardened or is it still soft? If it is still soft, I would try butyl first.

[Joe & Cherie]

It is very hard. I had to use a razor blade and a scraper to get it off. Once off I could bend it a little bit then it would break. It seemed like some kind of caulking. But, even tho it was a real pain to remove off the fiberglass, it barely stuck at all to the rubber ring. Which may be why it leaked in the first place!

I can’t help but wonder if it isn’t already proflex on there!?!

[mary and bob]

This type of tail light mounting, the rubber ring, is commonly used on big trucks and trailers. In those situations it is not necessary to get a tight seal, so no sealer is used. Probably a poor choice to use on a fiberglass camper. The benefit is they are quick and easy to install the lights. Can you convert to a flange mount type of light?

[jimknoch]

Originally Posted by Joe & Cherie

Awesome! I’ll look into those! I hope Lowe’s has em! Thanks for the tips, I was so unsure on this one. Gotta admit I don’t like the setup. Rather have hard external lights but I already have the big hole so I can’t change em lol.

Joe & Cherie,
I would give some "3M Weatherstrip Adhesive" a try. Available at most auto parts stores. It used to come only in a bright yellow, but I think it is available in black and clear now. This was the best adhesive to use on weather strips in cars some 50 years ago. Good luck with the issue ... Swampy

[Iowa Dave]

Originally Posted by jimknoch

Joe & Cherie,
I would give some "3M Weatherstrip Adhesive" a try. Available at most auto parts stores. It used to come only in a bright yellow, but I think it is available in black and clear now. This was the best adhesive to use on weather strips in cars some 50 years ago. Good luck with the issue ... Swampy

I agree 100% with Joe and Cherie. I’ve used this product to seal submersible boat trailer tail light assemblies for 50 plus years. I’ve always used black. It’s easiest to use if it’s not too warm at which time it gets kind of gooey. So don’t leave it in the sun when you’re about to use it. Room temp (about 70 degrees F) works best for me. Takes a little scraping with a narrow plastic putty knife to remove but will peel off the rubber without destroying the sealing surface.
Iowa Dave

[Rzrbrn]

I have tried a number of different sealants. If it is applied to neoprene then Lucas 100 Neoprene Rubber Sealant, if is a butyl rubber gasket then DAP 27062 Caulk or CRL 777 Butyl Rubber Sealant.

I really like the 3M products. These are ADHESIVE sealants: 3M 3000 UV, 3M 4000 UV and 3M 4200 fast cure. Note that 3M 5200 is a permanent bond adhesive, so use only if you really don't ever want to remove it.


Occasionally I use Amazing Goop, but it is a silicone caulk. It comes in very small tubes, which I like. I found this somewhere:

Amazing GOOP® and Craft GOOP® contain a thinner formula for precise, detailed work.
Wood & Furniture GOOP® is a thicker, non-slump formula perfect for vertical and overhead applications.
Automotive GOOP®, Household GOOP® and Plumbing GOOP® are all the same formula.
Lawn & Garden GOOP®, Marine GOOP®, RV GOOP® and Sport and Outdoor GOOP® are all UV-resistant.
Shoe GOO® is a more rubbery formula allowing for greater flexibility.