Almost all of them are, if you're willing to pay. Expect to pay on the order of $400-$800/month for a bare basic cabinet with minimal power/network in one of these facilities. You can put whatever you want in your cabinet, doesn't have to be computer equipment.
Good point, you could store a 2U, and the upside is the ability to communicate on the network if the box gets opened. Virtually no chance to lose network connectivity.