CM Wasson, The Brompton dealer in Palo Alto Cal carries a bag to shoulder the folded bike in.
there is a wheelie bag that Brompton sells and one that is a dust cover when folded , carries in a seat bag on the bike keep the place it's stored clean.
someone sewed a heavy duty canvas bag that came with My Bromton used purchase .
so there are always commercial sewers to call on , awning makers often have side jobs that they will do.
+ sail makers where boats with sails need repairs..