The important part of the install is on the dry core. Cutting an appropriate-sized hole, and using rubber gasket material, will give you a good, waterproof grip on the dry core. You CAN just leave the sport skin uncut, or you can cut a small hole in it to allow you to access the cap on the p-valve. If you do the latter, be sure to cut the hole FAR smaller than you think will work. The skin stretches a great deal. I would also highly recommend either burning the hole in the first place, or doing something to reinforce the walls so the unraveling cannot continue.