I use a plain paint scraper for household use (the kind with the wood handle and the four-way blades that are held with a screw in the center) I grind the blade to a rounded surface. This is what Rob Max recommends in his manual. It's cheap and works great. You could almost finish the entire inside with it. You have to keep it sharp by hitting it with a file. Then I hand sand with a sanding belt wrapped around a soup can (about 60 grit) I'll go to a finer grit in the cockpit area and under the hatches where it will show. I wet it down with a damp cloth to find the glue traces. It's too bad you didn't know this. good luck.