On Friday, March 16, 2018 at 6:51:50 AM UTC-7, wrote:

...Harbor Freight stuff is too cheap

For final finish, maybe. But I've found that the standard $16 purple gun ($10 when on sale) is perfect for spraying the vinylester we use as an in-mold primer instead of gelcoat. I generally get three good sprays out of them, and then relegate them to backup duty or the parts bin.

For the polyurethane topcoat, the auto body shop down the road uses whatever they use. Probably pricy.

--Bob K.