OK so here is what I did: I first roughly cut some packing paper to a little larger size and pushed it into the opening to take the imprinted shape of that space, I marked the edges with a pen, then took it out and cut with scissors, creating a paper template, which I used to cut the mat to size. If I then just put it in there, it stays, but it's not stable and tends to move around after the door opens a few times. I then removed the adhesive cover and tried to attach it that way, but it is hard, since it can't be put cleanly over the spot, it has to slide into place, and with the adhesive it's impossible. I had to cut it into several sections to make it doable, and it's still not perfect. I will just redo it more carefully later, but for now I will drive around like this to see if it makes a difference.