In 1985, my wife, young son and I took my mother's 1971 VW Bus camper to Oregon and back. It was fun and easy taking our home on our backs, tortoiselike. That vehicle was a favorite for many in those days--compact but full of room, and with the hard extended roof, there was room for sleeping--and you could stand up in it.
Nowadays, the Bus is an historical relic, but one company is putting expandable roofs on Honda Elements. Although the last Element was just built a couple weeks ago (see blog post), there are hundreds of thousands you could buy and get converted by Ursa Minor Vehicles.
It's a great platform for it, and the cost seems reasonable. I wonder if you could rent one?