a friend/ colleague of mine lives in a Ram Promaster. She has a large AGM battery and a bank of solar panels on top of the van, with a charge controller and inverter inside. The panels can be raised for better efficiency, but she tends to keep them flat against the room for stealthiness. By and large it works okay, though a spell of cold cloudy days can run the AGM down to the point where she can't run her little fridge (60W). I built her a backup bank of LiFePO4 batteries that she can charge at work to run her fridge, but she hasn't really got the hang of that for some reason. You'd be able to run a small lathe (Sherline, 7x14) or minimill of that easily.
Downsides - fuel economy sucks, I think she gets around 18mpg highway as she's basically driving a giant brick. Also you're looking at a pretty significant chunk of change - her van cost her $50,000 all set up and about 2 to 3 years old.