On the other end of the spectrum might be a diesel westfalia camper, maybe good for 30mpg, dunno.
course if you just want a place to stay dry and keep the bears off ya, then a mat in the back of your hatchback (passenger seat forward) can be relatively comfortable.
And a jungle hammock fits nicely on anything from a bicycle on up and is quite dry and comfortable.
Though it would be interesting to see an eco'd bus
