Curiously, there is a discussion going on over at the Fiberglass RV forum about exactly the same subject. Here is a post by a guy who has sprayed gelcoat on the outside of his old Boler fiberglass trailer:
I did spray a new gelcoat as part of my restoration.
It does require a spray gun that is able to handle the thicker medium. A gravity feed system doesn't really work but I purchased a gun type that was designed for it. Had to mix a batch the size of the can on the sprayer (add catalyst) then spray that. Then mix another and spray,etc. Purchased a 5 gallon pail of gelcoat that was colored to match my trooper by the manufacturer( used over half). I still have to sand / polish the finish to get the very smooth high gloss that is possible. But I am thrilled with the result so far. It is a little stippled like eggshells or orange peal but a sanding with very fine paper will flaten that out and polish it. Repairs now can be done and sprayed with gelcoat and polished to match...
The body had developed hairline cracks and other things that required fiberglass patching so I wanted to get it back to a fiberglass finish instead of paint. But a professional paint job should be a great finish... Just didn't want to spend the extra $2,000 that would have cost. It cost about $500 for the gelcoat, spraygun, etc. and quotes for a professional bodywork and paint job were comming in over $2,500.
Only took about 1/2 to spray once I did all the prep work - that took a lot longer......
Here is
his restoration blog.
Andrew