We contemplated this many years ago when the toyhaulers were first coming on scene, early-90's. None at that time were even close to being able to carry the amount of weight we required. So we went a different route, we chose to go motorhome and pull an enclosed trailer. This worked great while racing and then morphed into our current setup. It may be something to consider. By the time you look at the investment of a large toyhauler and a truck to tow it safely, you are as much money as a nice little older used diesel pusher coach that will be more than capable to handle the weight. We are on our third coach and second enclosed trailer now and love it, we haul our Harley and Jeep in our 26' Haulmark Edge. I love towing the trailer behind the coach but for some trips the trailer isn't a feasible option so we flat-tow our Jeep.
I did see a guy last summer in Ouray, CO that had a 34' 5th wheel trailer and then flat-towing a really nice LJ behind that. He said it towed and handled great, but I had my reservations about it.
Mike.