Well, I agree. While 40 MPG instant economy is quite do-able, 40 MPG average is quite improbable for these vans, (or any, I presume) without some serious mods.
Theres a DSM club in omaha and one of the guys has an OLD turbo caravan with I think a saab 9 3 turbo on it and its set up for atmosphere venting...a spooling and wooshing caravan is definatly a way to turn heads.