Sliced a big piece of 5mm foamboard into a 90 degree curved board today. Used Evo-Stik wood glue - worked in the past - and small veneer pins to hold it together. I will remove the pins and encase the sides and ends in thin ply when its all set solid. This is to create low walls to stop things diving to the floor as well as to add to the stiffness. The track should probably go on an underlay of some sort. I'm thinking that the neoprene route is probably better than cork as the latter is quite heavy.
It is remarkably light and level. If you hold one end [in one hand!] there is only a slight amount of twist - perhaps a couple of mm over the length. I think this half proves that with some proper support or legs it will be more than rigid enough. Will need to test that with the heaviest stock I can find!