How do you match the thickness? I measured Scalextric track and found that it is some odd number between 1/4 (0.25) and 3/8 (0.375). It was something like 8.2 mm or 0.323 inches. Not an industry standard thickness in plywood/MDF. I thought about getting a drum sander to make the match better but $200+ was a little steep. In your experience, does the height difference impact the cars riding the apron? If the apron is low do the cars de-slot easier when the rear wheels drop onto the apron, or if the apron is high do the cars hop when the rear tires bump against (and ride up on) the apron?
For HO I saw Bryan's solution of using double sided tape and one layer of HO cork rail bed on top. That created a real nice apron. I've thought about the foam rail bed as it is about half the cost of cork, but I'm not sure if the tires will have more friction on the foam and won't allow a nice power slide, plus I'm concerned the rubber tears up the foam.
George
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"Get the shotgun, Martha. The herd needs a thinnin'." - Bucky Katt