Question about wet sanding

[wellcraftv20step]

Morning all, I've been getting the boat ready and I'm at the compound and wax stage. I normally compound the hull with a product called Buff Magic which in my opinion is a great product, very expensive but like anything else you get what you pay for! My question is this, just above the rub rail their is that 3or 4 high section of fiberglass and it's very chaulky and rough like it's really been neglected. It's a tough place to get the polishing wheel on their from both the top side or from a ladder so I was thinking I could just wet sand it with some fine/very fine paper enough to knock it down a bit,then compound it by hand. Am I going in the rite direction with this and if so what number papers should I be using,thanks