Dieselpuller... Welcome to the forum. Hanging out here is a great step in working your way to an HDT. I know there are a few people with HDTs that are planning on being in Quartzsite sometime this season and I'm sure they will pop in here. While I'm not in Quartzsite, I am about 85 miles east of you right down I-10 and 2 miles south. I have a 670 which is the same depth sleeper as the 610/630 models, just about 3 foot taller. The 770/780 models are the same height as mine but about 13 inches deeper. That extra depth is mainly used in the size of the cabinets but does allow extra room if converting the interior. If a max size sleeper is high on your priority list, the 770/780 model is the way to go. With that said, if you've got nothing to do sometime, drop on by and I'll give you a tour and a demo ride of a 670.
Ray