I broker used wooden and metal storage containers as well as vaults. Containers are more substantial than vaults because they need to withstand the rigors of a lot of handling.
The equipment I broker usually has been previously used in the mobil storage or self storage businesses.
Both metal and wood containers are very sturdy and are bolted together. Usually they are about 5' x 8' x 7' and weigh more than 700 lbs. And they have hinged doors that can be locked, are stackable, and shed water.
The containers are transported on a flat bed truck and a fork lift is needed to load and unload them.
Used storage containers are an inexpensive way for a mobil storage or self storage operator to increase revenue. Buying used equipment is also an inexpensive way for gaining entry into the mobil storage business.