I have sometimes been able to reseal these by removing the excess old dried sealant around the edges and putting a new coat of “self leveling” RV sealant on it. You won’t be able to find it at Lowe’s or Home Depot. Go to an RV supply store and tell them what you need to do and they will sell you the proper sealant. It usually comes in a tube like a tube of caulking and it is cheap. If the old sealant is in really bad shape you may want to go ahead and remove the vent or fixture so you can clean all the old sealant material off then reseal it with new material. Some fixtures may need to have a strip of butyl tape put under the sealing edge before you screw it down. Butyl tape is also cheap but it is only available at RV supply stores. It in combination with the self leveling sealant will stop any leaks
. I am sure the sealant Bigfoot
is recommending will work.
The best way to remove the old dried sealant is to get a variable temperature heat gun to heat the material which will soften and loosen it so it can be scraped off. A heat gun is like a hair dryer but it blows REALLY hot air. A hair dryer will not get hot enough. The reason you need a variable temperature heat gun is so you can set it on a lower temperature that will not damage the fiberglass. I wound up buying one of these from this company:
Along with the heat gun it works best to have a hard plastic scraper of some type to remove the material. You have to be careful. If you try to do it with a metal knife or scraper you will damage the fiberglass. I did find a hard plastic paint
scraper at Lowe’s for about three bucks. Plastic ice scrapers are not tough enough. A polymer knife would also work. I did a quick search and found these Steck brand hard plastic tools:
I don’t have these but if I do any more trailer windows
or vents I will get them.
You will also probably have to have a screw driver with square drive bit for the screws on the fixture. When you are replacing screws in fiberglass do it with a hand screw driver and be gentile. A screw gun might strip it out.