The guy who did my camper back recommended 303 Aerospace Protectant for the clear vinyl.
He said never use soap of any kind on the clear vinyl, just water than apply the 303 product.
Used it about 3 times last summer and the vinyl windows stay clear and pliable, seems to work great!
It’s hard to not soap them down after a salty trip, but he said just resist the temptation and the vinyl will last much longer.
I spray it on than smooth out with cotton cloth, than just leave it to dry; next day the vinyl looks like new.