I have a solution to both Andree's & Donald's problem. Hire the local 
homeless guy to watch your van. If you let him'her sleep inside, you'd even 
help alleviate the homeless problem.
 I have several Vanagons parked in various places in San Francisco Bay Area. 
So far none has been broken into. It probably helped that I didn't have any 
fancy sound equipment in the dash. In one car I intentionally left the old 
radio wires hanging out the hole from where the old radio was stolen before 
I bought the van. Works like a charm. Oh yeah, I donate a few bucks to a 
couple of the local homeless guys once in a while. Much cheaper than an 
alarm. Tehy even notify me when the local cops tag me to move my vehicles 
around.
 Cheers,
BenT