So after wet-sanding the crap out of the boat last week and letting it dry completely, I finally got up the courage to try another coat today. I stirred the paint extra long (just to make sure) and then, as-suggested, added a small amount of Penetrol - maybe a capful or less for the paint needed to cover the whole 11' boat. It was like night and day the difference. I think maybe I finally understand how rolling and tipping is supposed to work. Even before tipping, the paint was beginning to even out, which it did NOT do at all my first coats. After running a 4" bristle brush after the roller, it blended fairly well, and I can't see much for curtains or sags. It was like a totally different painting experience. It still won't be show worthy, because I couldn't sand it totally smooth without going through the filler, but I may be able to paddle it in public now... if people keep their distance...