Some folks do and some folks don't... apparently.
Personally between expeditions I leave my kayak in an all-over kayak cover called a "Garage". They are pretty expensive if you were to buy one but mine was left behind by the previous owners when we bought our house so it was pretty much free. The good thing is it has a SPF of over 50 so UV is not a problem and is waterproof and largely windproof - it certainly keeps my kayaks, boat and fishing kit in pristine condition.
I am more interested in what other people on this forum apply to their cars to protect them... you see, the attractive and functional ferric oxide finish on mine is beginning to flake off and leave unpleasant stains that look like rust stains on my driveway.
I am wondering what I can do about this before it gets too bad as I fear that in the long term it may have an impact upon the vehicle's ability to transport me and my kayaks to exciting new destinations not to mention its resale value.