Once you have a strong enclosure it's important to make it as smooth as possible before you start to paint.
1. I took a big piece of cloth fiberglass and several ounces of resin and covered the entire enclosure with a near-seamless layer of cloth fiberglass. This make the enclosure super smooth and an extra layer of strength can't hurt.
2. After the resing has hardened trim all the excess fiberglass ans sand down as much of the high spots as possible. I used 80 grit sand paper.
After everything has been smoothed down you can either primer it right them after preping it w/ acetone (the path I kinda wish I had gone) or get some bondo and try to get a perfect surface for paint.
I went with the bondo, but so far I havent gotten it any smoother than it was before I added bondo. The layer of cloth really does make it smooth but flowing bumps is what I wanted to get rid of.
3. I bought 1 quart of Ultimate bondo from wal-mart. Prep the surface of the enclosure with 80 grit sand paper. Then clean it with water then Acetone.
4. Mix the bondo according to the directions and spread the bondo over the enclosure filling in holes, gaps, indents, ect.
5. Sand all the bondo down to a smooth surface after it hardens. Try not to sand all the way through if you can help it.
6. You will need another layer of bondo. I made my second layer thiner than the first. Pour out some bondo on a mixing tray. To make it thinner just add in a little acetone at a time untill you feel like it's the right viscosity. Mine was thin enough to spread w/ a paint brush which worked really good. You should be good with paint brushed by now and have some laying around.
7. Once the thinner bondo is mixed just brush or spread it on like the first layer but you may not need to add bondo everywhere, just to low places that need it.