You do understand that the TRV sensor head senses the air temperature around it and closes or opens accordingly , it does not measure the temperature of the water or the towel rail, so as soon as a towel is draped over the sensing head it will shut down as it will think the whole room is at the required temperature, you have went to the bother of buying a decent looking rail, you asked for professional advice on the installation, many have told you the same thing , like many on here disregarding the correct advise means more work when you discover that those that do this for a living are correct, and just because it is not what you want to hear does not make what you want to do work