Tony, if that barn doesn't already have a slab that you're going to build on, DEFINITELY consider slab heat. It's so nice when working near or on the floor.
If you're in the Anchorage area PM me and I'll give you my buddy's number. You should give him a call and go visit him. He built a garage a while back and is still working on improving it with things like a compressed air system. It's only a 2-bay, but without all the stuff that he has in it, he could get his fifth-wheel RV in it, along with the tow truck. John's concern about burying things would apply here, but he uses the back of the bays for miscellaneous storage, and he has a mezzanine in the back of one. He lets me use it just about whenever I need to. My garage at home is full of my disassembled '51, much to my wife's dismay, as her car sits outside all year long.
