Hi Mittelwaechter,
the original VIIC manual (
http://www.uboatarchive.net/Manual/Manual.htm) states at page 50:
"G7a can be stored in all places except auxiliary stowage, because there the engine chamber would be positioned at the support point.
G7e can not be stored in both deck containers and in aft reserve stowage because access for maintenance is insufficient."
Regards, LGN1