[mitiempo]

Sand the hull where you want to attach the backing board and wipe with acetone to remove any wax or remaining paint. Mix epoxy and add colloidal silica to thicken it and place on hull. Place board where you want it and tape with duct tape of similar to hold it in place until the epoxy sets. Youn can go over the edges with glass tape and unthickened epoxy resin if you wish but it probably isn't necessary. I'd also seal the wood with epoxy. Here's a link to the use guides on the Gougeon's site (West system) but any reputable brand is fine.
Brian

 

[mitiempo]

You can use a flap wheel on a drill, a wire wheel, or as I did the little sanding drum on a dremel with a flex drive. The flex drive lets you parallel the hull with the sanding drum and it's small enough to get most of it. You don't have to remove all of it, just most of it. Here's a pic of the results when I glassed in two partial bulkheads in the galley.
Brian