I would think if you covered anything, it would help block the suns UV rays and that is never a bad thing. I cover my tires when home, even if we are home for a couple days and then take off again. It's not any problem covering and uncovering the tires with properly sized tire covers.
About your dash? I see folks in parking lots putting sun screens across their windshields in the cars all the time, mostly in the Summer, to help keep the sun from heating up the inside so much. They just fold up when done and tossed in the back seat.
If not in use, covering is always beneficial against UV rays. The only exception may be covering the entire camper and then you plan to use it again soon. Covering with an RV cover and removing it repeatedly over the winter is a real pain in the neck. If the camper sits though, covering is beneficial.