Although I really do feel for the OP and appreciate his post (and all the interesting comments on this thread), I am a bit bewildered about one thing.
Regardless of where we are camped, if it's just an over night and trailer never gets unhitched, or if we've been somewhere for a week, before moving the rig one inch, I walk around the entire rig at least once and check everything. sometimes I circle the entire rig twice (which drive my wife batty, so I just smile at her). I check to make sure the locks are all locked, antenna is down, all the caps are on everything, everything bungied down, tied down, locked down, hitched right, tires look good, all the pins in the hitch are in place and a pranskter did not pull one on us. I even do this when parked in a parking lot and we've gone inside to eat something when on the road. If we stop at a rest area, before leaving, I walk around. There again, checking to make sure a prankster did not pull the pin on the hitch, or leave a glass bottle under the tires, or anything out of the ordinary.
Call me over protective, but I do this so routinely now it's just part of doing business. Too much can happen on the road. Not to mention what a thief or a prankster may do to your camper at a campground (which IS possible).
My question is? Didn't the OP do a walk around the camper when he pulled out of that campground? If he did do a walk around, wouldn't he have noticed the tire gone?
I never though about it until someone hit the idea on a post (above). More than likely, it happened by a thief when the camper was parked in a parking area, when traveling, and he was inside a store.
Most RVers know the value of tires and such. But some kid or redneck gang of kids might not know the difference. It's possible they took the rack and tire because a bolt cutter can easily cut through those bolts very quick, where-as taking the time to unscrew the 2 lug nuts holding it onto the rack probably takes longer.
If it was "kids" that took the tire, I bet they were disappointed when they found out the RV rim is attached with 6 lugs, whereas most autos use 5 lug rims!