I totally agree with Tom T on using ripped 3/4 plywood as your framework. I did exactly that with our club's display layout years ago, and the sections show no sign of warping or bowing. I screwed and glued all sections when assembling them. We don't walk on our sections, and were interested more in light weight for ease of portability and transfer from trailer to set-up site. That's why we used 1" and 2" foam for the tops. Here are a few photos of the construction:
The sections are held together upon assembly with carriage bolts and wing nuts. The legs (again for portability) are 2" pvc pipes with carriage bolts on the ends for adjustment on irregular floor surfaces. Again, not for walking on, but with 3' widths, it's not necessary.