Thanks to all who responded.

I did hear back from the BMW dealer, and they say that even if you remove
the plastic tub bolted to the bottom of the new 3 series trunk, there is
still no room for a spare tire. DOH!

Can anyone confirm this (without tearing out your plastic tub)?

If I really want to ditch the runflats, I will still need a spare regardless
of whether I go with summers, all-seasons, or winters. Maybe I just plop
the spare in the trunk. Yeah, 30 extra pounds of rubber and rim, but, I get
peace of mind.

Bimmer should really have given the buyer a choice. Ah well.

Mike