If you aren't able to be plugged in, DampRid is the excellent choice. Available at WalMart and WalMart online. Put a few cannisters around the RV and check on it every couple of weeks.
There is another trick: Get one of those disposable aluminum baking pans and lay down a layer of cat litter, then another layer of DampRid and that will last a little longer.
I really wish RV mfgs got the clue that the reason we all want to cover our RV's is to protect the roof. Why they can't make a snap on roof cover is beyond me.
WoodGlue