Are you concerned at all about that middle/back edge "flopping" back over time since it will not be clipped?
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Looked again and no. The back that goes up to the seats is very stiff so I don't see anyway it would flop over. That being said based on your concern I did take a clip slid it over the top edge of the mat and bent it to fit under the seat.
Not sure how well it would prevent possible "flopping" but am sure I could take care of any potential problem since you can lift the seat up. Hope this helps.
Will be interesting to see what Weathertech eventually delivers but these will definitely keep the rugs in better condition then Weathertechs. However looks make a difference and some will prefer the Weathertechs and some TuxMat.
I'd really like to hear from TuxMat Model S/X owners. And I have no relationship with TuxMat and never heard of them until someone posted about them on the forum.