I’ll throw this suggestion out to you too – while a warm sleeping bag would be a good start, maybe a couple sheets of plywood to put over the truck bed with a tarp over that would provide you some extra protection from rain/snow and also trap in some body heat. You wouldn’t have to make them permanent and could just slide the wood into the bed when not sleeping under it. A cheap bivy as Ryan suggested would also be a good consideration and a quality sleeping pad to provide some warm rating and comfort from the truck bed.
There is a profound difference between a good idea and a thriving business, but as the saying goes: “A journey of a thousand miles begins with a single step.” At a certain point, turning your dreams into reality is as basic as putting a plan in place and, step by step, making it happen. The good news is that there has never been a better time for starting and learning how to run a small business.