Thinking about converting and ambulance to an RV

You COULD make a decent class B from an ambulance that is on a full van body, such as a long WB high top Sprinter.

Box on a cab and chassis is probably a waste, as others have noted, you will invest time and money in appliances, fixtures, cabinets, etc only to not get any of it back at sale time, in addition to being run out of campgrounds.

The vehicle is probably great for making a service truck, but not so much for a camper.

Charles