Paint
I used 3 coats of Rustoleum after I made the lightening holes. I read somewhere this made sense, but don't know why. I don't think the temeratures are high enough to require high temp paint, but if your box is near a heat muff or exhaust stack I may be wrong. I guess if you are really interested in loooooong term protection from heat and battery juices, a high temp epoxy would be best. I your wallet full of green stuff? If so, go that way IMHO Best CJ