I kept my rig at a seasonal site this summer. Just a simple do at home, inspect the roof and wash it regularly. The frequency that is needed to protect and keep it clean depends on the type of trees it is under (pine sap, seed bearing trees, etc).
I do not keep my rig there over the winter as I bring it home, cover it and leave it in my yard. If I were to leave it at my seasonal site for the winter (which I could if I chose), I would cover it just as I do at home. I would also make sure all underbelly and other holes are filled with steel wool to keep mice out.