Well... heck... do it! Just post pics of rthe results! It probably would look good and be easy to touch up like you said. Makes sense. When I coated my floorpans with POR15 I thought about it but didnt use the chassis coat, it turned out nice. I can post pics and part #'s tonight if you want.
Also, I picked up a cheapie spray gun ($6 bucks) from harbor freight and used it..then just threw it away.