Hi Andrew,
I would STRONGLY consider trying to buff the
fiberglass instead of
painting it. I also have a
Trillium 1300 (1980) that was very oxidized. The finish was so bad my hand would get chalky just touching it.
Here's what I did:
1) Wet Sand with 600 grit sandpaper.
Wrap wet/dry 600 grit sandpaper on a sponge
dip in pail of soapy water
sand in a circular motion.
keep dipping to wash the sandpaper clean
Wash really good and check out the work
This sandpaper is so fine it won't scratch the finish. Actually makes it shiny once dry. if you're scared at first, try in an inconspicuous spot - maybe the roof.
2) use a product like this one that I bought this product from WestMarine.
http://www.meguiars.com/?boat-rv-kits/Fibe...toration-System along with a power buffer from a home store
If you have a boat store in the area, check them out. They will likely have this or some similar (mildly abrasive) product.
Using this technique and some elbow grease I was was able to get a really good shine to it. Just do one side at a time. (don't forget the roof) You might be able to buy just the Meguiars # 49 cleaner then finish with any old car wax a little cheaper.
I figure if I keep it waxed, I should never have to do that again.
This was much cheaper than
painting it and I don't have to worry about peeling
paint in the future. The
fiberglass was designed to be bare - not painted. You'd have to get all that oxidation off before you painted it anyway or the
paint would not stick.
Good luck. I'd share my "before and after" pics but I don't have any "after" yet.
Oh- regarding the deep scratches, again, check with a boat dealer. WestMarine (not I don't work there) has a scratch filler that come with color dye you mix in to get a match. Might be a little tricky unless you're an artist but I bet you can get it close enough.
1975 Trillium 
Trillium in hybernation
Linear Mode
