TCjeff, you probably can get by with a gasoline SRW.
The question is do you want to get by or have plenty of truck. I think get by means watch how much you are carrying including how much water you have and how full your holding tanks are, and watch how much other items you carry.
You’ll definitely feel the Rockies and any steep mountains with the gasoline trucks. It’s hard to say how well the 7.3 will work since it isn’t released. However, it sounds like you aren’t going to pull anything and a gasoline truck might work fine. Diesels have a big advantage at elevation since they have a turbo.
When carrying the TC, the biggest concern of gasoline is the lessor range. At the same time, gasoline is readily available at every service station.
If you are looking new, I’d seriously consider a 4x4, CC, DRW in either Chevy, RAM, or Ford with the largest gasoline engine of each. 4x4 in case you need it, CC for the extra storage or people ability, and DRW to carry more weight. I don’t think the Ford 7.3 is out yet and I don’t know if the Chevy 6.7 is. I’d wait if you can to drive those before committing to a smaller engine if you go gasoline.