After more searching, trying out other brands of luggage, figuring out if I could reinforce the B-bag... I just gave up. I ordered the B&W hardcase. Thanks to all the forum members who helped out with information.

BTW... I phoned one dealer who said they had just tried to fit the Brompton into the Tern Airporter Mini, and they said "no go". The internal padding doesn't allow it to fit. Ah well.