However, my first approach used only one pipe topped by 2" of blue foam. I routed out a groove down the middle of the foam that would nestle over the pipe. The foam was attached to the pipe using construction adhesive. This approach worked okay for straight track, but for curves I had to cut the rigid foam into short sections and piece them around the curve.
For this layout, I wanted all the advantages of the PVC pipe approach without the hassles of "foaming" the curves. So my version 2 approach was to use two parallel pipes and then glued homasote on top. By using the pair of pipes they provided about a 2" wide surface to support the homasote. This approach worked fine with a couple of cautions...
To install the pipes I built "T" risers from 3'4" plywood for a riser and short sections of 2x2 for cross pieces. I had previously marked the track center line on the top of the benchwork. I screwed these risers to the benchwork along the marked center lines so that the top of the T risers were at the correct elevations. Given the benchwork design, these support risers are spaced 12 to 16" apart.
I remarked the track center lines on the top of the 2x2 portion of the risers. I put four 1/4" nuts over a dry wall screw to provide a "fatter" post, then screwed this combination to the 2x2 on the centerline. These "fat" screws provided a row of posts for the PVC pipes, one on each side, to nestle against. The posts kept the pipes in alignment. I clamped the pipes in place and then screwed each pipe to the 2x2 cross piece to hold the pipes in place.
