The short answer is ‘no.’ In some circumstances, parking outside is a better trade-off than hangerage. It depends on the environment and the usage of the aircraft.
An aircraft made of any material will deteriorate if kept outside, uncovered and unused for long periods. The wood structure of Robin aircraft is superior to metal and man-made composite because wood does not corrode. Note that Robin offer an unrivalled 20 year warranty on their airframes with unlimited flight hours, so no concerns about weather damage there!
Crazing of the paint on the upper wing surface due to aerodynamic lift is now eliminated by the Swiftwing, which helps to maintain a waterproof surface. So, all that will happen If a Robin is left outside is that the paint will lose its gloss more quickly, just like a car that is parked outside.
Condensation and ultraviolet light are the main two problems for all aircraft kept outside, irrespective of their construction. Condensation can cause corrosion in many areas; airframe, avionics and engine (although the plasma coating of the bores of the Continental diesel engines provides protection even there). Ultraviolet radiation will attack paint, composites, perspex and avionics. A full set of covers will protect your aircraft against the ravages of the weather, will prevent water ingress to the cabin and will reduce ultraviolet damage. Flying the aircraft frequently, avoiding parking for long periods on grass and using dehumidifier gel packs can help keep condensation at bay.
Hangerage is good if the environment is harsh, the aircraft is used little and the hangar is well ventilated but, just as for a car, putting a wet aircraft away in an enclosed space with inadequate ventilation can be worse than leaving it outside!