Before you go the sanding route, may I recommend another 3M product called "Marine Restorer and Wax". I used this on mine 1986 and it totally brought the boat back to life. On the label it says:
"Designed to remove HEAVY oxidation, chalking, fading, minor scratches, rust and exhaust stains; plus provide protection on fiberglass/gelcoat. Available in liquid and paste versions."
I used the liquid version. What made this even more awesome, I only needed to apply once, one coat on and buff out. It goes on a bit thick and takes some effort to wipe off, but one coat and I could see my reflection on it. My recommendation is to do small areas at a time. Like as far as you can reach side to side without moving. Then buff off before moving to the next section.
Thoroughly amazed with this. I used this for two seasons now on the hull and this season, switch to there normal wax now that I got all the oxidation out. Even the professional guy that was working on some other boats was amazed how good it looked when I was done. Not the cheapest wax, I think it was about $30 for the big bottle, but I only needed half to do the hull of my 32 ft. Mariner.