Can't say there is a "rule of thumb" answer to your question. To me, the top was meant to be down! Condition the plastic with one of the spray products out there. I use Plexus. Make sure the plastic is dry when applying. I keep mine down for 1 week and then raise it for a day or two and apply the Plexus. Mine shows wear right in the middle where it creases when folded. Don't think you can do much about that over time.