We bought a cover for our 179 this year. We left it uncovered last year and had no problems with rodents etc but we wanted the extra protection from New England winters so I bought a cover. We store the pod at our dealer and they put the cover on for us. It cost $235 +/- and it is made specifically for the 179. It has an excellent fit and an access door so we can get in and out in the winter if we need to.
To avoid insects etc, we cover all vents on the outside and I left mice bait inside. We are picking the pod up at the end of March for a trip to the Florida Keys so I will know better then how it works out. I can't imagine you would have more of a problem with pests with the pod covered rather than uncovered.