I know very well a guy that restores/rebuilds soft tops - and his advice is NEVER use any protective layer on a soft top.
Hartz, (the manufacturer of the fabric) say the cloth is specifically designed to absorb water and wick it away. This ensures the cloth stays supple and in shape. Water won't enter the car as there is an impervious membrane within the fabric.
It's fine to clean the fabric using specialist cleaners, however it is NOT fine to "treat" the fabric with anything that is water repellent or which cases water beading on the surface. Why? Well because this causes the fabric to dry and go hard - when this happens you create the conditions for the fabric to shrink, the fibres prematurely age and start to get damaged, and the lack of suppleness to the fabric then creates issues on the runner, motor & mechanics of the roof.
Of all the soft-top products you can use, he tells me Renovo is the worst - its effectively a swear word as he says it creates and almost bitumen style coating on the fabric which cracks and causes untold damage to the roof itself. Actually it's great for his line of work - he makes money replacing roofs that have had such products used on them, but he'd never recommend use of any such product.