We have two (Himiway) E-Bikes at 72 lbs each, and a Hollywood carrier at
53 lbs. for a total weight of 197 lbs. That said, I would be concerned with the amount of torque that it would put on the hitch with a 10 inch extension would cause going over bumps while driving.
If there was a way of tying back the bikes to the rear of the RV to keep from a flexing that should work.
That's the reason why they do not recommend bike carriers on the back of TT's. They also don't even recommend them on the back of Toads which make no sense to me. If you can have them on the back of a Jeep but not a towed jeep, How does a Jeep (and Carrier) know that it's being towed