I used to have a cover on my Grumman that was parked outside. It was a Cambrai cover of breathing material so there wouldn't be as much risk of condensation underneath (www.cambraicovers.com/). However, there still was some condensation (not damaging though) and the worst problem was that it would strain against the OAT probe and chafe a little at the straps in strong winds.
In the end I decided I was better off without the cover. The weather in The Netherlands does not carry much risk of sunlight damage, but your situation may be different.