I only use my Z4 for pleasure only on sunny days 2 - 3 days out of the week. My question is...would it harm the top keeping it open while the car is not in use, rather than opening it and closing it every time i use the car? I am worried that keeping the top open for long lengths of time will do damage to the fabric and lines. Want to increase the life of the top motors by using them less. Was thinking maybe once a week or so. Any thoughts?