It is highly recommended that a plane of this type be hangared. Sure, the fiberglass is mostly impervious to weather given proper finishing and appropriate treatment with carnauba or better non-silicones like Rejex, but the plane has a multitude of little metal parts that will suffer. These planes are typically not water-proofed against rain and condensation and moisture will find its way to the metal eventually. This is especially bad near the salty coasts.
Now, having said that, I keep my plane on a tie-down. It has a cover and during the worst of the winter, it will be taken off airport and stored in my garage. Hangar space is almost not available and if it were, I couldn't afford the $600/month rent. So it basically comes down to do you want to own this plane or not. I did, so it is on a tie-down and I will be facing much increased maintenance and possibly more frequent replacement/repairs of parts and equipment. Not the best situation, but not the worst either.