Deflate them, roll them up and put 'em in a storage compartment....lots of RV'ers go with the inflatable type kayaks like the SeaEagle brand.
Once in a while I see the kayaks mounted vertically attached to a rack at the back of a MH or 5th wheel.
I've also seen a specially built rack on the roof of a crew cab that extended out past the cab at the front and had posts down to the front bumper. The kayaks were tied down to the top of the rack. I'm sure they blocked the view of overhead signals.