I've been wanting to put in a Teak Shower mat for a long time. I've read all the threads concerning it and the different approaches, but I decided to modify this one to fit:
Pretty simple to cut the length down from 31 1/2" to around 23 1/2". Then, removed the end rail of the piece I cut off so I could use it later. Then a partial cut about 6 1/2" from the cut end, providing clearance for the wheelwell. Lastly, cut a piece of the saved bottom rail to fit, and reattach it. The mat is well built, and comes with stainless steel screws - no glue.
Just a bit of sanding to do on the cut ends, and a touch of Teak Oil. I think it turned out good. Hopefully my estimate of the size (using Bob's photo with the mesh 12" x 12" black tiles) will work out, since I don't have access to my trailer right now. It's not quite deep enough given the estimated 22" depth of the floor, but one or two inches of wiggle room is fine I guess. I'll post a follow up photo once it's in place. I may replace the black rubber feet with white ones, to prevent any marks on the shower floor.