I've had far more success finding E150 Conversion vans with low miles and low rust than I have E350s with the diesel or even early models with the Windsors. I've pretty much ruled out any modular engined vans.
I cant seem to find any builds of conversion vans. I know they are just RWD, but for those of us who aren't going far offroad, that's good enough for me. They also commonly have a high-top which is nice as it allows a taller sleeping platform.