Thanks for the input guys. I have a call in to my supplier and will most likely go with his recommendation or abandon the idea.
Good move. They should know both NFPA and DEP requirements for your installation.
If you want to do some reading, check out NFPA 30 Flammable & Combustible Liquids Code. Chapter 6 deals with Container and Portable Tank Storage.
6.1 Scope.
6.1.1 This chapter shall apply to the storage of liquids in
drums or other containers that do not exceed 450 L (119 gal)
individual capacity, in portable tanks that do not exceed 2500 L
(660 gal) individual capacity, and in intermediate bulk containers
that do not exceed 3000 L (793 gal) and to limited transfers
incidental thereto. This chapter shall also apply to overpack
drums when used for temporary containment of containers that
do not exceed 230 L (60 gal) capacity. Such overpack containers
shall be treated as containers as defined in 3.3.7.