Outside of normal condensation I don't see why you would have a problem. I use the
Weather Guard boxes and have never had a problem. Some of my boxes are pushing 20 years old and are still in daily use. They outlast the trucks.
We do put a rubber mat in the bottom, IIRC it is the stuff they sell at Tractor Supply, it is about 1/2" thick, cut it to fit. Main reason we use it because the guys like to throw things like axes and mattocks in there.
Aaron