I've even seen some based on Mark I Escorts, Subaru 360 Sambars and Hillman Imp vans... and there is a Bedford CA Dormobile with rare left-hand drive in a wrecking yard on the East Coast of the US that is very tempting, it's very small too.
I could not imagine sleeping in a Sambar or an Imp. The Bedford is the smallest one I could stand spending any more time than, say, a swap meet or music festival, living in.