Bucket
That is covering my mast hole in the deck. I first duct tape it with UV resistant duct tape then stick that tub over it. With a keel stepped spar you get gaping hole in the deck when you pull the mast.I note this with curiosity as I have sometime thought of placing one of these overtop a cowl vent that otherwise has let in snow. Kinda defeats the purpose though. Let us know what function you tub has.