Frank D. in Montreal
I apply a very thin coat, just enough to wet the surface (not a lot of finish in my brush). I admit that I have probably never been faced with your conditions (90 degrees and low humidity). I'd thin it out (water it down) 10% if I had trouble applying a thin coat, so it would be a thinned coat. The goal of the last coat is just to get rid of the sanding marks while not leaving new brush marks.