Greg,
I have a 33ft Gulfstream Ultra 'Super C', which uses the GMC 'Kodiak' C5500 Medium-Duty truck chassis.
It has a towing capacity of 10,000lbs and is available with a Duramax Diesel or 8.1 gas engine. Either engine is backed by the Allison transmission.http://www.gulfstreamcoach.com/ultra...perc/index.htm

They are priced no more that 'van-based' C's, and other manufactures are now using the same chassis. (Jayco, Four-Winds)