Hmmm...interesting. You'd need electrical input, and a water source.
I wish there was a way to put a solar panel that would generate enough watts for the grow ...on the roof, or how about a solartube? google it, there are tons of links.
http://inhabitat.com/2006/12/28/solar-tube/
You'd have to do something about the ventilation and the heat buildup. How many watts would the pump and fans and hydro stuff pull?
The van should be parked somewhere discreet. If you drove around with it and got pulled over by CHP, welll:
Officer: "What's in the van?"
PerroSucio: "Well officer, it's a traveling botanical educational exhibit."
Officer: "Mind if I take a look?"
PerroSucio: "Uhhhh...."
Sounds like a fun project.