Aha! Sometimes these guys direct us to do some of the screwiest things...so basic that it seems hard to immediately answer why it is wrong.
On the gas...we do weld HDG brackets all the time (outside) so I knew about that. Good comment though.
What I proposed to the Eng. was nipples thru the wall (wall is 6" thick with ins. core and galv. skin) with O-Z Gedney CDS? sealing bushings (the feeder is 3-500mcm per phase in tray up to wall on either side). Then have mechanical guys flange/seal around conduits as they see fit (I think we can get them pretty tight). They are worried about thermal loss. This is a cold storage building. Or a EYD with Chico on either side.
Thanks for help. I haven't even had time to break open the code book till just now. Crazy lately...working 6-7 days most weeks. Wife is real happy....