I'm putting some V-spar Flagship varnish on my Pygmy Coho. Just when I think I have it right, a sag develops in the night. I'm putting it on with a foam brush straight out of the can. I plan on using it for a boat, if you know what I mean, so it doesn't have to be a work of art. I'm not going to use 5 different grades of paper between coats (I use Scotchbrite), but I want it to look good. What's the secret to a sagless shine?

Peter