Like the last poster commented, probably already got it figured out, but diesel is the only way to go. I couldn't imagine trying to pull 16k or so with a gas burner. You're on the right track with a Cummins for sure!!
If you wanna go HDT, check the links below for all sorts of info, but it'll be pricey by the time you're done. Jack's site talks about a company that makes em custom. Single the tractor, put on a big sleeper, all sorts of stuff. I just marvel at the expense, but have no interest in a rig that big...or a Smart car as my transportation once I'm camped.
http://www.rvnetwork.com/index.php?showforum=32
http://www.jackdanmayer.com/