[frizzen]

I've never done a glass layup for something in this size, but you're going to have issues trying to get any of the corners of the mold to come out right.

I would try to make up a female mold, so you'll have much less finish work. Use fiberglass mat (not cloth, it won't be as flexible). Youre going to want to spend time breaking up the mat enough to get it down into corners. I wouldn't mess with gel coat until you know if you can get a reasonable pull from the mold that won't take finish work.

I might even try to go with a can of the 'fiberglass reinforced bondo' instead of doing a layup. It's harder and stronger than pink bondo, and shouldn't put up as much of a fight to get the corners to take, or the inside smoother.