Harold:
Any 'rated' wall cannot have a membrane (sheetrock) penetretion exceeding 100 sq inches, per 100 square feet, as I understand.

Surface mounting is acceptable, as long as there are no penetrations exceeding the above behind the panel.

Jurisdictional responsibilities are building along with elec, plumb & fire dependent on what the item is.

Sorry for the delayed response, I missed this one as you posted it.


John