I used cork roadbed that I stained grey under my tubular (o27) track. I nailed it to the tabletop with an electric brad nailer instead of gluing it down. It has the toylike look I was going for. I also used extra ties from 3r Plastics. Here's a shot of what the end result looks like:
This is about 5 years old. The cork has shrunk a bit, in that you can see an occasional seam, but it's not too bad. Working it around the curves gets a bit tricky with the tighter diameter curves, but the 42" wasn't bad. The 27" curves took a lot more brads to hold it down, as it wanted to buckle in some of those.
The cork I used came from Midwest Products, and was about $1.50 per 3' section IIRC.
J White