I had made a sliding intake door for mine in an effort to save money. It works, but I wish I'd used a ball valve instead.
I would add wheels, but I wheel the thing around with a dolly and set it up on bricks while cooking, and that works just fine. I do wish I could find time to add a small table to the side.
The UDS works great. The only problem with the UDS is the airflow after you open the thing. All that extra oxygen gets in, so you get a big slump, then a big spike in temps if you're not super quick. You have to shut off all air flow for about 15 seconds or so before you open it up to mess with stuff to avoid the worst of the spike. As a result, I don't usually mop whatever's cooking, but I don't think it's necessary, especially if you're foiling.
Ideally, you would segment the top and bottom of the UDS with something to restrict air flow and act as a heat diffuser. You would need to cut a door in the bottom side of the UDS to add/remove fuel that way, though, so it complicates the simplicity of the UDS, and that's really the whole point.
I leave my UDS outside all the time. I don't have any rust issues. I spray the outside with cheap bbq paint from time to time, and fatty pork does the job on the inside for me.
I had used a 22" grill lid for the lid on my drum. I have a scrap piece of bent aluminum and chunk of metal I use as a exhaust rain deflector - I just use the metal chunk to keep the aluminum from falling off. Looks ghetto but works great. I don't get any water inside at all.
I use an old coffee can with holes in the bottom as a firestarter chimney. I start 9 or 10 chunks of charcoal with a propane torch. Everything comes up to temp in roughly 30 minutes or so after I start the coals. Once I'm at 220-ish, it doesn't take very much airflow at all to maintain temps.
I use a big tinfoil roasting pan on the bottom of the lower grill as a deflector. It cost a buck and it works great. I just used a little steel wire to hold it onto the grill. I poked a few small holes in it to let juice drip through. Keeps things cooking nice and even. I don't use a water pan, I haven't found it to be necessary in the UDS.
