Just finishing up the painting. On the inside of the quarter panels, after checking the assembly manual as to what area is supposed to be covered, I put on two coats of Spectrum Sludge a day apart. The stuff dries in about one hour, but, so as not to mess it up I waited one day.
You can brush it on any old way, then, "dab it" - quickly working with the brush at a 90 degree angle to get the right finish. OK, it helped that I have an unrestored 67 GTA right there to copy from. A day later I primed it, no primer soak in. Two weeks or so later I painted white over it and again, no color soak in.
So, to summarize: no paint gun necessary at at. All you need is a nylon brush. 2-3" wide is suitable. Remember to "dab it" at a 90 degree angle.