Well Sal, that is the old cookie cutter method which is still hard to beat. You cut the roadbed out, elevate it, and use plaster and something for the ground. It's still a hard to beat method. Gluing up foam also works. Man, there a so many acceptable ways to do it that threads like this often become Ford v Chevy things. I agree that 2 and 3 inch foam is ouch,$$$, that's the biggest reason I haven't used it much myself. I like the cookie cutter and shell method too, because I'm cheap. LOL.. BTW, Shamus is redoing his fantastic On30 layout and he used... the cookie cutter method. He used 1/2 chip board with 1/2 sound board (simular to homasote) on it for road bed. He then used weaved carboard strips for the base for his plaster. I figure if it's good enough for him its good enough for me.
But seriously, I use ceiling tile wire (bailing wire) and 3 inch masking tape with plaster soaked paper towels over it. The mistake some make on paper towels is they use the good expensive ones they steal from the kitchen. That's a horror story, use the cheap brown ones on the roll like you can liberate at the gas station, or if you can't find the chaep brown ones, the 3 rolls for a buck and a half wallmart ones are fair. But Bounty sticks in a gooey ball when soaked with plaster water. I love that broken arm cast material too, but it tends to get $. I think I would pass on laminating foam sheets together because I bet if you add the price of the sheets and glue it costs more than the 2" or 3" stuff net. The foanm I use I get at appliance places and construction sites and doing an little dumpster diving on ocassion. Besides, you can make better times in the alleys at rush hour anyway. The other day I found a old 30 inch solid oak door in the trash, perfect shape. I also have found load locks which I sold at the truck stop in 5 min. Boards, whole sheets of plywood. A back window for an S10 which the salvage yard gave me $50 for, the owner put in slider and threw the old one in the dumpster, a 2004 model? All on my way home from work driving the alleys. But that's prob more than you want to know. Have fun, Fred