To John R,
Spray adhesives (do they still make "Formula 77"?) Basically a rubber cement-like contact cement. If the metal is clean, as by a wipe of acetone, these work well. And, when the sandpaper is worn out, heating - e.g., $Kote gun - softens it to allow stripping the paper off.
Naphtha - "Ronsonol" type lighter fluid if you can't find a better source - cleans the glue residue off. Messy, but it works.
I've made several sanding blocks of common 1 by 2 wood. I cut them short, the length of a standard sheet of sandpaper. As long as the wood is flat, straight and smooth it works for me. Longer blocks require longer sandpaper. A Sharpy marking on a cut end records the grit on that block.
I'd be leery of the edge butt joints of shorter lengths glued up..