What kind of cleaner and protectant can you use for a fabric top? How often do you clean and protect it?

Washing, normally I just spray off at home with water. I have used a bucket of soapy car wash and a soft brush. At a power car wash, I have heard can cut the fabric if you get to close?! Caution.
For protection I went to the BMW dealer and purchased their product. It was a bottle of stuff that you mixed with water then sponged onto the top and allowed to dry. Most of the time my car sits in the garage so it still beads up after several years. Sometimes I get little strings and cut them off carefully.
Mine has a plastic rear window, it fogs over and can scratch easily. I used a really fine polish and had good luck using it softly. Caution here too.
1995 e36 318i convertible.