I actually used a can of "fiberglass resin jelly" rather than just regular resin because the regular resin was sold out. Gave a bit of additional thickness to the fleece. I coated it inside and out. After it cured, I used bondo-hair to thicken it up further, then sanded it mostly smooth. Then I did two coats of bondo, sanded in between to try to cover up major dips. Because I'm going to cover them with some sort of fabric or vinyl, I didn't really sweat getting them perfect. I'm probably going to modify the boxes a little bit for the subs to push them back a bit. They are a very, very tight fit.
Like I said, cheesy paint and unfinished because I'm thinking of making some slight modifications before I cover them for good.
Here's how it turned out... The two 12s are actually a little TOO loud, so at least I don't need to run them full bore:
