I was doing some re-arranging of "stuff" in the room that holds my model railroad, when it dawned on me that moving the three modules that I had previously built out of 3/4" plywood, each weighing 40 lbs or more, was just too much of a pain. My previous layout was started under the same philosophy of modular construction, with the intent of keeping those modules "forever". While lifting those 40+ lbs modules of layout is currently physically doable, as more and more delicate track, structures, and general scenery items are added, they have to be treated with much care. That is hard to do by yourself when they are that heavy and bulky (3' x 4'). So, I made the monumental decision to completely start over again and build a new layout. This one would be made out of a lighter material, the modules would be smaller, but they would continue to conform to my plan for the overall (future) layout.
I had previously experimented with all sorts of foam board material to try to build a lightweight, modular layout. All those foam-based experiments failed as most foam materials warp over time. The only one I had not tried was Gatorfoam® board. This was because it is extremely expensive stuff, which is why I decided to go back to 3/4" plywood as the base material for my modules. However, I visited a very large N-scale layout in the Houston area where the owner had built his layout out of sections of 1/2"-thick Gatorfoam board, then placed each of them on a wooden sub-structure, and connected them together to form the large layout. So, I did some extensive research online and found a company that had a reasonable deal for ten sheets of 3/16" thick, 2'x3' Gatorfoam board. The ten-pack arrived in the mail today, so the new layout is officially a "go" now. Below are several links to others whom have used Gatorfoam for their layout's construction.