I've found the best paint to use is on a fibreglass trailer is Interlux Brightside. You can get it at a Marina (paint is used on fibreglass boats). I've painted my Trillium
1300 with it twice in 12 years, does not peal and is flexible, self levelling (you can roll it or brush and tip, not recommended to be sprayed). My trailer is left outside and paint will fade a bit after a few years ( stored in side would be best ).
They don't have Trillium green, but I have mixed the color using their yellow, black and white paint. It was 5 years ago that I painted it last, so I may be a bit off but I think it was close to 5 parts white, 2 parts black and 3 parts yellow (adjust may be needed)..
I contacted Interlux recently about adding Trillium green to their color chart, as it would probably be a popular color with all the vintage trailers getting restored. They responded with a they will look into it, thanks.