I looked first at those self healing mats, but didn't really need the functionality of them as a cutting surface, I was able to order enough rubber to make 6 of these for what the same sized self healing mat costs.
This is one of those times that had me considering a table saw purchase. The lip is a bit higher than I'd wanted, my original plan was to cut some 3/8"x2" in half, but it took all day with the tools that I have to make one piece that I didn't bother. This would have given a very tiny lip, just enough to keep those pesky screws from wandering too far, and still be able to work comfortably. All that's left for me is to sand down the rough edges and maybe a bit of a finish to smooth it up some more.