I always (well, almost) hand wash my smoker stuff.
(Almost because I did put my racks and mats through the dishwasher once recently.)
The water pan seems to work for me OK as a catch pan.
I learn most things the hard way, and once did a smoke without it. That made a mess, dripped stuff on the element, and generally stunk things up.
But I always do something I learned from daveomak, I run my MES 30 at 275° for 2 hours, after I've cleaned the racks and mats to sterilize and dry out the smoker box.
Then, before I'm going to use it again, I put my tray of pellets in it, and run a pre-heat at 275° (for 2 hours), which re-sterilizes it and dries out the pellets, too.
Never any WhatzThat growing in the smoker following those before and after steps. (And no smells to attract rodents. It smells unappealing to them.)
Dave suggested that to a poster who discovered mold in their smoker. I think it is good preventative maintenance.
I tried foiling the catch pan for a time. But now I just wash it good and heat treat it.
I was impressed with how clean the dishwasher got my racks, mats, and water pan. But it kinda had an Oh-der for a bit.
The wife never mentioned it, and it was gone after the next run. But it made me nervous.