While I do not doubt that the tables shown there work well, they would take a few minutes to put together and break down.
I use a piece of 1/2" plywood with a piece of rigid foam insulation on glued to one face of it, and it works really great for a cutting surface for my Festool saw, and the router.
Bill, your idea of the foam core sandwich sound good, the only thing I might be tempted to add would 1" thick solid strips all the way around, this would make the whole thing a LOT more rigid, without adding a bunch of weight, but just the foam might be enough?
Keep us posted!
The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
William Arthur Ward