jake:
It sounds like there is a bit of confusion somewhere regarding the term "Protection"
"Protection from physical damage" , and 'Overcurrect Protection"
There is NO dimension within the NEC, and I do not believe there ever was a specific measurement. IF SEC is 'inside' and NOT directly (Closest to the point of entry)into a MOCP device it must be encased in a min. of 2" of concrete on all sides. As I said, PVC, EMT etc. does not count.
A main panel, located either outside, or inside closest to the point of entry of the SEU solves that issue. In THAT panel, you land the grounds which bond the neutral there. Now, from that panel, you run SER (4 conductor) fed from a correct sizes circuit breaker to your SUBPANELS, each with a separate ground block. Make sure your main panel is capable of accepting the size (amperage) breakers you need for he subpanels.
The assumption is that this job has only one (1) utility meter.
