The TR tonneau came in two flavours. The first, which I think was a dealer option attached to the top of the windshield, for storage/parking outside with top down, not for driving with, kind of useless. The other I believe was an aftermarket product that attached to the front of the dash where it meets the windshield. Because of the slope of the windshield, hard to get at but doable as LastTR showed me at this years Portland ABFM.
Personally I would just put the top up or down as required (unless your top is 31years old and a little stiff, requiring hot/warm weather or a hair dryer to heat up the vinyl a bit so it can stretch.) No way I'm going to replace the top when it still looks like new, even though it takes more effort to keep in touch with what the weathers going to do.
TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra
