Lots of new class Cs are coming with a 7500lb tow rating. Prior to that 5000 was pretty common, 3500 sometimes as well.
I have an older 30' class C on an E450 that was originally rated for 3500 lbs towing. I took it to a heavy truck shop, had them reinforce the frame and add a 10k hitch, and they said it would be safe up to the GCWR/GVWR and axle ratings. Which comes out to around 7-8k depending on how heavy we pack.
I pull a small two horse that weighs around 5500 lbs fully loaded without issue. If anything, I've noticed that the motorhome is MORE stable with the trailer hooked up.
My biggest problem is ground clearance. I need a 6" drop hitch for my trailer to be level, which hanging waaaay back of the axle means I need to be extremely careful about any large bumps or inclines so that I don't bottom out.