New at the whole Beekeeping thing but have been a contractor for years. In my experience, go with a 4" cigar roller to get the paint on and then have someone else come right behind you to brush it out... Its called laying it down. Makes a smoother finish, but i wouldnt use my sprayer because although it coats it fast, it does not obtain the same MIL thickness as a roller will....It would take two or three coats with the sprayer to get the same protection that the roller will give. Roller= longer life for your boxes. 8-)