I unfortunately had a about two years where I had to park outside, it did a number on the plastic (cowl, radiator grills, etc) but if you keep a good coat of wax on it at all times and take care of any water spots asap (before they get baked on), you don't have to worry too much. Definitely buy a good sunshade, and condition the leather dash ever now and then.
You might also look into something like this, that just covers the cab, but is quick to take on/off:
Accessories for the Porsche Boxster and Carrera by Roadster Solutions