I have a MX-5 ( Miata ) and the top isn't cloth but some kind of vinyl. I use 303, or Mothers protectant on it. Neither of them last very long. I would say less than 1 month and the weather better be good.
One thing tough, the roof looks very good when the stuff is freshly applied, and that only worth the effort but it give a false sense of protection. The roof of our TT is obviously not made from the same stuff but the environment is the same and I dont beleive at all that these stuff can do anything other than making the owner feel good.
I can see one thing tough, when I wash and scrub the roof, it comme back real nice and its surprising the amount of dirt that is collecting on it. That must be the same for our TT. One thing for sure for me, I will clean the TT often and watch the caulking, thats it thats all .
Jayco Whitehawk 24RBS 2014
Ford F 150 Ecoboost Tow Max 3.73 2014
Equalizer hitch 1000/10000