I modified a 45' Kingsley Coach a few years ago with great results.
If you start with a ful height garage, you can build a bedroom with the bed over the hood of the car. This gives a lot more room and really a full motor coach type of layout, that is Cab, living room, galley, bath and then not just garage, but bedroom. See outside pictures in my album under Cobra.
My next project will involve a Motorhome with garage but with the car carried on a slant with just the front wheels over the rear truck tires, and a Beaver Tail door/ramp to get the car in. Above the car at the very rear will be space for a few, 3-4 motorcycles that will lift up to the ceiling and be above the car when everything is closed up.
I will also use 2 super slides in either side up front, and will have the bed over the car hoo as in my last conversion.
My last coach was built on a T-2000 with a 10 speed autoshift and a Cummings N-14+ 470 HP engine.
It rode like a dream and had all of the power that you would want.
Or anybody thinking the same way that I am?