I was thinking along the same lines as richkae. You can drive from campsite to campsite and charge up overnight.
Me too. In fact I've started looking at cD and frontal area for various vans, hoping there will magically be a large van with low drag. No such beast, of course; it would be nice if somebody built one as Rich describes.
I've got a '97 Ford Econoline with a Sportmobile Class B pop-top conversion (so the floor isn't as low as Rich's ideal; but it's not any taller). .37cD (pretty typical), but of course still a pretty big hole to punch through the air. I haven't yet started calculating how many batteries I can get it to carry...but even after taking out all the gas trappings, it probably won't be much over 100kWh. So maybe twice the energy of a Roadster; but with a LOT more drag and weight, it's definitely not going to be able to do 200 miles.
It would probably work for in-state camping. But then again, so does stuffing a tent and sleeping bag in my Roadster's trunk and cargo box. I suspect this will just remain a dream.
Some vans I've glanced at, with their cD and height x width; multiply 'em together for a rough approximation of drag:
Dodge Sprinter: cD .36, 78" x 93" (Sportsmobile will put a pop-top on it)
VW Westfalia: .51 (!), 73" x 81"
VW Eurovan: .36 (regular model, but MV is probably not much worse), 72 x 76
2000 Econoline: .37, 80 x 79 (Sportsmobile will put a pop-top on it. A university put on a smooth belly pan and reduced drag 15%)
Bright Idea concept: .30, 79 x 79 (a year or so ago I asked Sportsmobile to try to be a "fleet" buyer and put poptops on them; Sportsmobile has a facility about 50 miles from Bright's)
Last-gen Toyota Sienna: .30, 67 x 73 (GTRV will put a pop-top on it). This definitely has less drag--but of course it has less room and ability to carry batteries, too.