Cheap

I came across for Used ocean cargo containers for sale. Some have multiple roll-up doors which could come in handy.

Offered by Steve.

Look in the yellow pages under trailers. If you live close to a port city or trucking hub you'll find thousands. They can be had rather cheaply and shipped to your door. Our used 20' was $1200 and water tight. These are also known as intermodal containers.

http://www.truckandtraileronline.com/trailersearch.cfm
http://www.mbi-trailers.com/sales/container.shtml

Offered by Michael.