I would check the Escapees Forum. There are a lot of HDT guys there.
I for one wouldn't want one. Imagine the camp sites you couldn't even get to, let alone backed into! Besides, I get 12.0-12.5 mpg towing my 5'er and I have read the HDT guys claim 7-8 mpg towing or not towing.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof