I am into year 11 with my CS 17. It lives outside on a mooring all summer, and under a snow tarp in the winter. Water will eventually stand in the bilge if left unattended for a while. I did have a little rot in the ply (starboard side of floor, bottom near center, just aft of the CB trunk) where the bilge water sat and the paint system failed. Hindsight being 20/20, I would definitely apply a layer of 4 oz on any surface that may have standing water on it. Do the Floor up 6" from the bilge on cockpit sides. even the deck and seats could benefit from a light layer of cloth to keep the paint system intact. I hate painting.
The repair took no more than a couple of hours over a couple of days and I am fortunate I got it early on. Good as new now and raising hell off southern Cape Cod.
On a side note, I added a Yamaha 4hp with an external gas tank, and loving my expanded range. Now, just need time to sail!