I scrub the grates and then oil them. Left alone, mine started to rust and pit. The smoker (used the way I smoke) never gets hot enough to burn the stuff off the grates.
I also empty the ash and of course scrub out the water bowl.
When storing it, set the middle section upside down. The seams on the cover are not water proof and putting the middle section upside down causes any water that gets inside to run down on the outside rather than accumulating on the inside.