Haven't decided on which shop vac yet, but I thought I'd share some brilliant ad copy for one of the 14 gallon Ridgid model on the Home Despot web site:
"For your added convenience, the patented car nozzle attachment cleans out the back of your truck to make room for your tools and equipment."
That's a lot of vacuum-size dirt in the back of a truck. Not enough room for tools? Sand storm, maybe? :-)