We have towed a trailer behind our last two fifth wheels. First was a 2011 Springdale 242 and current one is a Cougar XLite 27RKS. Both had "custom welded receivers that attached to multiple locations on the trailer frame rails and the rear crossmember that supports the trailer rear wall.
We tow one of two trailers. First is a Bass Tracker Tournament TX 175. Package weight with 20 gallons of gas and tackle is around 2200 pounds. The other trailer is a 8x14 aluminum flatbed trailer with the Slingshot as cargo. Total weight is around 2800 pounds with a full gas tank on the Slingshot.
To date, we've accumulated around 25,000 miles towing one of the two trailers behind one or the other fifth wheel. No problems and no structural/skin/wall damage to the RV as of this date, however, I'd urge you, if you do consider towing behind an RV, be sure that you have a quality rear camera mounted on the RV. It's very difficult to monitor what's going on behind the RV and it's quite possible to lose the cargo, lose a tire on the second trailer and not even know it until that next "bathroom break" at a rest area.
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS