I made an important discovery last night while rolling the umpteenth coat on my trunk: It really helps eliminate runs if you don't load the roller up with paint very heavily. Instead of rolling it through the pool in my tray like usual, last night I tipped the tray and moved the pool to the end while running my roller through the runoff left towards the top. After that I squeezed a bunch out on the tray and then went to work. I'm sure a lot of you have that down already but for anyone who's dealing with runs on vertical surfaces, just try going really light on the paint, where you have to really push hard to get coverage. The tip of my roller was still whitish while I was working.