SeaDek (and maybe others) will make it thicker. The 9mm is pretty hefty - maybe go even thicker. You could make it "wall to wall" by doing your own template. The only problem is that it's not available in wide enough widths to cover the whole cockpit in one piece so you'd probably need two - with a seam running either fore/aft or abeam. I don't know if they recommend a way to permanently seam it together? The "wall to wall" part would do most of the "keeping it in place" but a few well placed snaps/snads/velcro would be all you'd need to make sure (especially at the seam if it was still two different pieces).Its just 3M tape. Ya, it'll probably rip and need heat and a scraper.. I don't think it would be that terrible. Not like deck paint.
heheheh....WD40
I wish there was a company that made a decent one piece cushioned mat with a teak look. Cover the entire cockpit , all hatch seams and ports. Tapered edges. Heavy enough to lay down and not need any fastening. Similar to a work station mat but UV resistant
Haven't found that anywhere.