I use the same as if I were sanding a trimmed board, 200, 400, 600, 800, and 1200 grit. Also make sure the sandpaper you use is the waterproof kind, don't use the shitty white backed sandpaper.
if you want to skip sanding and just want the shiny finish, you can also go for XTC3D which gives the glossy finish and takes away layers and imperfections