I pull the foil from the top of the smoke box and bottom of the smoker. Wipe those down well with paper towel so there isn’t grease, dump the coal/ash from the box. With my 3D, I only leave in the grates that I am using, so when cleaning up, I fire up my gas grill and place the grate on top and let it get hot, then knock it down with the grate brush. Let it cool, put the grates in the smoker and cover it up.
I’ve had my smoker for 4 years, I’ve never had to do anything else to the inside. Others on the board use a paint scraper to knock off any Black seasoning that is flaking off and that may be about it.
I’ll clean the outside after a few uses with a stainless steal cleaner. Pretty easy to maintain compared to other smokers.