Make sure your vinyl windows are extremely clean each time you roll them up. They are so soft that any dirt left on them will scratch the surfaces & eventually leave them cloudy.
Likewise, to keep them from getting cloudy/yellow, NEVER use paper towels to clean them. Never ever. Paper towels are made from pulverized wood products and they leave a bazillion little tiny scratches behind each time. Eventually they build up into a haze, then to the point the window becomes opaque and then yellowed. You've seen them like that. From having used paper towels on them. Only use slightly moist cloths like old bath towels, cotton tshirts, old soft cotton diapers, etc. to clean them.