Have you looked at the Dodge Sprinter? I think those are about 20' long in total, give you about 6' x 10' on the inside and ~25mpg. I'm actually crazy enough to think that's big enough if you can manage without the shower or any kitchen setup. Obviously you won't be hosting any parties in that situation however.
A van alone would not be sufficient space for me, but I have considered converting a van to a small motorhome (either a Sprinter or diesel Ford E350) and using it as my tow vehicle for a midsized travel trailer. It's a weird choice, but it would solve some of my problems with my current rig (a 34' class A).
I'm considering a Winnebago View or Itasca Navion (or Fleetwood Pulse), which are based on the biggest Sprinter chassis in a cutaway form. They're a little bit smaller than I want, but I think I could probably live with it, given the benefits. They tend to get 13-17 MPG. They're a little on the pricey side, since I'll probably be paying cash.
I'd really like to have something small enough to be comfortable in cities, while still being large enough to really live in with occasional guests (I may be a loner, but I like having the option of inviting people to come with me sometimes). Stealth campers (converted buses and box trucks and vans) lately have great appeal for me, since a lot of place I haven't yet visited in the US are densely populated cities...so, being able to park on the street in the city without attracting attention would be very valuable.
I have more stuff than most folks would need (I have a small recording studio, three guitars and a drumset in my current rig), and I have a 60 lb dog. So, we can't go van-sized in any way I can imagine, without giving up a lot of my music gear. But, we'll see how it all shakes out. I've begun to get serious about shopping lately, and plan to move into a new rig in October or November when I get back down to Texas (I don't want to buy a vehicle up north where I'm currently parked, since they take so much more abuse up here due to weather extremes; California might actually be ideal, since the weather is so kind to vehicles there).
