230-70(a) says it shall be installed as near as practicable. That is the only thing the NEC says on the subject, which leaves distances up to local interpretation.
In VA each county is allowed to set that distance, most of them pick 7 feet. If it is back to back (or nearly so, as you indicate) it would be allowed here. BUT you may not be here
Suggest you call your local chief electrical inspector to ask what the interpretation is, an how far you're allowed to enter the building. This is an old argument, and I'm guessing they've already addressed it.
Personally, I don't think there is much 'structural' difference between the pvc and the sec.