Al,
I've got Gargraves/Ross track and have laid it on top of 3/8" anti-fatigue mat:
http://www.uline.com/BL_1751/A...ARg&gclsrc=aw.ds
I got a roll of it at Lowes but I don't think they carry it now.
I cut the roll into strips, wide enough for the track and so I could bevel the sides (using a bandsaw). It cuts easily.
I laid it on top of a plywood base. I've used glue, long staples, and currently zip-ties to hold the rubber strips and track in place (after drilling holes thru the plywood).
I ran trains for a long time before I put ballast down and things were quieter without the ballast. Some folks may disagree but now that I've got ballast down I can tell the noise level has increase. I may end up pulling it all up and spray painting the rubber with some gray texture paint (if I can find some that will adhere to the rubber) to make it appear it is ballasted.
At the time, it was actually cheaper per foot than cork roadbed, not sure what the cost would be now. A 36" wide piece/roll will yield a lot of roadbed!
Here's an old photo of my garage layout showing sections with and without ballast: