Just to add my $.02 to this thread; I saw firsthand one of the
Winnebago van conversions (NOT the behemoth one) this weekend. The one I
saw had all the options, and was super-nice. If I had $30k to spend on
one, I might do it. The inside was much roomier than the Vanagon
westy's, and the refrigerator was about twice as big. The cabinets
seemed to be laid out somewhat better. 
The owner (a fellow listmember) said that power was *no* problem
whatsoever. He said the van was happy cruising at 80mph, and he had
taken her to 100. Although she is quite heavy, he said there wasn't a
problem.
  Overall I was quite impressed, but as I could buy over 20 of my bus
for what that one cost, and there would be no hope I could ever do much
work on it, I think I'll stick with my split.
All IMHO
Richard