I have seen folding trailers from Yakima (their model is the Rackandroll) that might be storable in the travel trailer or a cargo rack (it folds up and weighs 150 pounds), then set up to be used for towing the blue boy long distances and on the highway.
Another idea is to get a rear hitch mounted to a travel trailer, use that for a hitch mounted cargo rack with a fold-out ramp. Carry the "blue boy" on that. Then, when you need to take the carrier to the dump station, move the cargo rack from the hitch on the TT to the hitch on the SUV, dump water into the "blue boy", wheel the carrier onto the hitch rack, secure it down, then drive to a dump station.