What have owners by using for the bottom half door seal? The very bottom of the lower door. Looks like a thin flap that simply scrapes against the threshold to seal underneath the door. I was anticipated installing a threshold door seal, but that is not what this is.

Any suggestions?

Turns out this is simply a door sweep of the cheapest variety and box stores sell something quite similar. Interesting though that Hi-Lo mounted it backward so the sweep seal goes under the door to seal rather than being screwed to the outside of the door. Makes for a much better seal. Clever.