I just done a quick google and this is what I came up with: Shroud Cover
If you werent worried about looks, Id just simply cover it with a garbage bag when its not in use. Anything to keep the dang Daubbers out of it.
Just another suggestion, while your covering you A/C dont forget to screen your hot water heater and your furnace. Id bet theyd be more prone to access one of the two of them before getting in your A/C.
Not that Id know that or anything.....