That 30-A receptacle might LOOK like an older dryer pattern, but it's not. It's a non-NEMA pattern common to RV-hoohups, and is a 30-A, 120V receptacle.
There's usually a breaker protecting the receptacle. Most RV pedestals also tap off this 30-A circuit to feed a 15-A GFCI convenience receptacle.
You never have 240-V available.
For what the OP wants to do, he has two choices:
1) He can but an RV pedestal, and mount that in the locker; or,
2) He can mount the usual sub-panel, then use the available circuits to supply whatever circuits he wants. Sub-panel with GFCI breakers is the only way to protect a 30-A. 120-V circuit.
It's been my experience that you'll do better looking for RV parts at an RV place, than at the electrical supply house.
As for Greg's picture of the fuse-protected receptacle: Phooey on that! "S" adapters? Fuggadaboud it! Instead, get an Edison-base 15-A circuit breaker. UL-listed, distributed by Bussmann, find at Home Depot.
