What kind of brush are you using? Your not going to be able to brush a door without leaving SOME brush marks. Sand after the first coat with 220, get you a good brush( I use a 3 in. Purdy xl sprig) Thin just a little if you need to and lay it off as smooth as you can.Latex is harder to use because it dries so much faster.You really have to move along at a pretty good pace to keep it from lapping.