I would go the used route. Gut it and build up your way.
Check out the Alaskan campers.
Popups have big plus and big minuses. Research what owners say. I loved the mpg mine gave, but hated the canvas sides that made it a tent. I sold it after less than a year. For a couple hundred bucks (I do lots of miles) in fuel I can drive a full size one and not have the minuses.