I could never get more than a year out of my tarps.
Of course the shrink wrap is only for one season too and more expensive than a tarp. But shrink wrap keeps it tight and mice free, if a mouse gets to work it can cost you 100's of dollars to get re-wired.
Since we had ours done late, I hope I didn't have a mouse in there before we had it wrapped, he'll be in there eating wires all winter, lol.
Ive always bought a box of moth balls and placed them in plastic cups around boat where they don't get wet have never had a rodent problem a old timer who is no longer with us told me this . Knock on wood.