Blimps in space - a question

I had an idea and was drawing it out: blimps and dirigibles with
spelljamming helms on board.  I drew up deck plans and was trying to work
out some specs, and I wondered about the tonage. would you consider the
airbag with the tonnage? It makes up most of the ship's size.

I figure it would count for a dirigible, but since on a blimp could be
deflated and put away like a sail, you would just consider it part of the
rigging.