You can find a Classic Accessories camper cover on Amazon for less than $200. It takes about 30 minutes to put on, 10 minutes to take off, and 8 hours to stuff back in the storage bag.
Might last 2-3 years. The fabric will start to disintegrate the 2nd year, so be careful pulling on it.
Still cheaper than a carport.
Wash the camper and allow to dry before covering it. Your choice of wax spring and fall.
I leave the "pass through" window open an inch or two and the cabover vent cracked open for some circulation.
