It wouldn't hurt to cover the A/C. It would help keep rainwater and assorted crud from building up inside the unit. A bag would probably work, especially since it would be for only two or three months, but there are covers made for the job.
Before you take the RV on the road in the spring, be sure to check all the roof seams, etc. to make sure no potential water leaks snuck up on you during the winter.
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Jeannie
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