Thanks. Some good things for me to consider.It certainly can work. If the bench work is true, then I would just put a bead of liquid nails (for projects) on the top edge of the 1x4, lay the foam on it and weight it until it cured.
Down the road, if you need to screw something to the bottom of the layout you can always liquid nail a small piece of plywood or block of wood where you need it.
It will be very lightweight, which means it will be more subject to unpleasant consequences in the event of unintended bumps, kicks and jostles.
I've been planning on starting the build in the spring for quite a while and it's almost time!