Looking for a used motorhome to tow 7000 lbs.

It depends on your needs. Ford increased the E-450 chassis to 22,000# GCWR with 14,500# GVWR. If you do the math that means you have a 7,500# tow rating. The drawback is many of these units only had 5,000# hitches. The reason for this is due to the frame rail extensions. You can have a sub frame beef-up done that will bolt to the Ford factory frame to upgrade the hitch and still be legal. The drawback is you still only have a 31' or possibly a 32' Class C. There are no Class A gas coaches anymore that can tow over 5K that I know of. That would mean you are into a DP or Super C. There are quite a few Super C units that can tow that much as well as DP units. You do need to work out the GCWR vs the GVWR. I.e. you subtract the actual weight from the GCWR and that is what you can tow. Most coach manufacturers do not provide the ability to be at your GVWR and still tow at the maximum GCWR. You sacrifice vehicle weigh to gain tow rating. There are exceptions in some of the Dynamax, and Newell coaches but in general that is what you will be working with. It can be done and with a diesel engine it will last much longer.