Fourty Foot!!!!!! you seriously need to rethink this whole thing if that is correct. Ok, I looked at the Keystone Outback website, there are a couple of 39 ft models, 10,500 lb Gross weight (which I calculated by adding the dry weight to the carrying capacity, they won't come out and say what the GVWR is).
Then I looked at the Michelin Agilis Cross Climate Light Truck tires.. they do not make a 22 inch in this tire. Biggest is 20.
Given that you have the potential of an 1100 lb tongue weight, or more, you probably don't need to waste the money on new rims and tires, just go ahead and jump right on up to a heavier truck.............
OK, getting the pop corn out and gonna watch this one.
Charles
Edit: Mitch and I were typing at the same time, he just beat me to the post message button.
'03 Ram 2500 CTD, 5.9HO six speed, PacBrake Exh Brake, std cab, long bed, Leer top and 2008 Bigfoot 25B21RB.. previously (both gone) 2008 Thor/Dutchman Freedom Spirit 180 & 2007 Winnebago View 23H Motorhome.