You may do better trying to find a "Used Tires" shop, since they are used to just doing the mountings and balancing. With the Class C, you don't have a "real" truck tire, so they should have the equipment to do the work.
Going to the bigger places that sell new tires, you may have a problem with them wanting to do the work
I agree with Biscuit, you should be able to park at any shop, unless they are slammed! Since I'm on the other coast, I can't really specify any particular places in your area.
Of course, you could just stick a knife into your tires, call Good Sam's R/A, and have then change the tires:B.....though I don't think that would be very ethical (no idea why it popped into my mind:H)
