Classy Chassis and Douglas both offer custom TC beds for cab and chassis trucks. With that budget and full time I would absolutely get a 5500. Yes, a 3500 with a gas ebgine, regular cab, 2wd, and no options will have a large payload. Most people don't want a truck like that. I love having an aluminum flatbed with tool boxes to carry my TC. But, I'm 1600 pounds over the GVWR on a 3500 dually.
As for solar, more is better. Aftermarket is usually cheaper. I'd get a couple hundred watts on there aftermarket, not from the factory.
