We bury propane tanks here in NJ also. 'Home heating oil' tanks are not very popular, major concern is leaking, and the nasty liability issue for polution.
Most of the diesel gens I know of have 'belly tanks', surface/above ground that the gen sits on. Gens that are inside tractor trailer boxes have a tank in the trailer, these are mostly rental gens, or former rentals.
Depending on the tank size, and GRHr, a contract diesel dealer is a prudent move.
