Many people camp in cargo vans or box trucks.. including myself. Budget is known to be one of the only burner friendly major rental companies. Their insurance will cover you on playa.
Not sure how you're planning on getting all the way to BRC. Are you trying to rent something in Canada and drive down? Fly/train part way and then rent? Cargo vans are sold out in Reno @ Budget but 10' and 16' box trucks are still available.
Not sure about the minimum age. Any questions, you could just call the location on Gentry Way. They're 110% very burner friendly.. no need to hide your intentions. Tell them straight out what's up and they'll help you out as best they can. Here's an excerpt from the Budget site:
"In most U.S. states, Budget Truck Rental locations rent to customers 24 years and older. Some Budget Truck Rental locations also may rent to customers between the ages of 21-23 with the following requirements:
Renters 21-23 years of age must present two valid forms of acceptable identification, a valid driver's license and one other form of ID. For details, please see FAQ “What kind of credentials do I need?”
At time of rental, an additional $18-per-day underage surcharge for drivers 21-23 years of age will be applied."http://www.budgettruck.com/faq.aspx#agereq
Again.. call the Gentry Way location in Reno
and see what they'll do for you. They may waive this altogether. They're that cool.
Check out this thread for some discussion that may interest you: viewtopic.php?t=35289