Yes, lot's of settling before we bought in '98 but surprisingly (and luckily) none to speak of since. I'm with you and I like jstroede's link to the deeper channel. I think that may be the ticket.
Here's a picture I thought i had up earlier.
The inside is actually most of the problem with making a form I think because the bottom of the door goes below the floor level on one side and above it on the other.
I considered what you suggest and just running the concrete into the garage and...
Just thought of that approach too! Maybe mounting the seal channel at an angle. Would have to fabricate something custom as you said because the existing channel is not deep enough to mount any way but flush.
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I recently (or should I say FINALLY) replaced an old one piece wooden flip-out garage door with a decent roll-up door. The flip-out door had a piece cut yo match the random gap at the bottom, but the roll-up door does not have that luxury.
My initial instincts say to go straight for concrete...
Stopped in several times over the years while looking for advice and ideas for various projects around the house and figured it was about time to join in the fun!
Current projects:
Fixing siding where woodpeckers have pounded out some pretty big sized holes.
Severely uneven garage door...