Hello ive painted fibreglass canopys in the past.
i've always used Zamix Superprime (just 1 coat needed)
As for a top coat: dulux weathersheild gloss.
I like to put 2 coats of gloss on but this must be done on consecutive days, hard to do with this weather!
Hello this is my first post too, hope i can help.
I am a professional decorator.
Lining paper is the best.
Sand, fill with an internal filler (not polyfiller) and sand again.
Size and line.
Hope this helps :)