Larry,
Knowing how the roofing felt expands and contracts on my shed roof, etc., is it really the ideal thing to use as a trackbed?
I know that it has a passing resenblance to ballast, but I've a feeling that it'll always cause trouble by distorting the track, due to weather-related movement.
With modern, near-scale track and wheels, it doesn't take much in the way of local 'twist' to mess up the best laid trackwork.
Just a thought ....
Regards,
John Isherwood.