When I need to be sure the cabinet, especially the seams, are flat and won't telegraph anything trough, I put 2 to 3 coats of epoxy on the cabinets after they have been sanded smooth to 180 grit. I sand the first coat of epoxy with 220 and the second coat with 320. If the cabinet is not completely sealed and smooth, I apply a third coat of epoxy then sand it to 320 also. If the adhesive you use needs more tooth to work, scuff sand with 100 or 120 grit before applying the adhesive.