You need a cover that will breath so as to not trap moisture
under the cover. Also as mentioned the truck has to be kept
waxed to protect the paint.
My son stores his 46 2 ton truck in an old lumber supply building
where years ago you would drive in one end and they would
pull out the boards from the sides and load it onto the truck.
Then you drive out the other end. This building is non climate
controlled.
Though there are cats that get rid of the mice but they like to
climb on the truck. There is also other people that store stuff
there and a artist/woodworker that makes some dust once in
a while.
What we do is use a fitted king size sheet on the top of the cab
and the flat sheet over the hood, fenders, and grille. It keeps
the truck clean and was done to prevent the cats leaving foot
prints. Though for some reason the cats do not like to climb
up onto the sheets.
He keeps his truck covered all year. At the end of everyday the
truck is kept covered. Even at the peak of his catering season.
Truck needs less washings and it keeps people from putting
their hands on or them leaning against the truck in the barn.
Of course we only use 100% cotton sheets so they will breath.
And better to use cotton flannel sheets because the heavier
material will better protect the truck. Jeffrey