I was using a piece of polycarbonate that was to thin and was allowing parts to warp by lifting the PC sheet slightly. When thinking about stable, flat surfaces I realized ceramic tile could be a nice surface. So I went to my local home improvement store and bought a 6"x6" tile and tried it both plain and with blue tape on it. PLA did not stick to it alone but with the tape it works very well. It is very flat and stable, with the only downside I can see being that it is a little on the heavy side.
After proving to myself that it would work I thought about options for mounting a larger tile and tested drilling and countersinking holes in a scrap piece of tile I had.
This also looks like it will work very nicely. My next step was to get a larger tile. The only problem here is that the Mendel print bed is not a standard tile size. However my local home improvement store will cut tile you buy there for free, at least small quantities, so I had them cut a 12" tile down to 9.5"x9.5" (which is a little bigger than the stock bed).
My next step is to drill the mounting holes, remove the wooden bed and mount my new tile bed. I am also thinking about adjusting the spring mount configuration to get a little more Z room and make the bed easily removable.
I may also do some testing with heating the tile as I think it would heat nicely as well.