I would suggest using a vinyl liner that has a ¼”foam backing. That should cover the remaining surface nicely. I purchased some from Sailrite. They have several styles to choose from. It comes 54” wide and is reasonable. I removed some vinyl hull liner that was about 30 years old. I scraped the foam off and then sanded the residue, coated it with epoxy, sanded, faired the surface again with epoxy and then applied the liner using a marine grade spray adhesive (3M 8080). That was over kill but it is all a learning experience right? I realize no one likes to work overhead but I have to believe that the results will be vastly more appealing and nautical than sand paint….
Good luck, Shanti