The panels all come e-coated. You can check them for straightness and/or shipping damage by checking them out under fluorescent shop lights. Any irregularity in the panel will show up as a distortion of the light's reflection. This is a similar method to that used with paintless dent repair and will reveal imperfections not readily apparent otherwise. If you prefer not to work on top of e-coat, you can sand it off with 180- to 220-grit paper, clean with PPG DX394 water-based low VOC wax and grease remover, and prep the bare aluminum by mixing PPG DX533 aluminum cleaner 1:3 with water and rubbing it into the surface with a gray Scotch-Brite pad. Let the DX533 stand for 2 to 3 minutes, rinse well with water, then blow and towel dry.