What's the best way to cover screw holes in pvc? I was thinking about filling them, then covering with a piece of plastic.
As BrownRedHawk suggested white silicone will keep water out (paint silicone won't accept paint). White latex caulking is similar to silicone, but it does cover easily with paint. You could also try 2 part white epoxy. This will set to a solid patch that can be sanded smooth and remain rigid and weatherproof. I'd favor the epoxy and once dry paint it with an appliance spray paint to blend it in.
get yourself a little tub of abs to pvc transition cement in white. using a brush, dab it in the hole and wait a couple of minutes for it to dry. then repeat until the hole is filled. you can stipple it with a fine brush to match the texture around the hole. you can also add some sawdust from cutting the pvc to the cement to thicken it up to make the hole fill faster.