okay you first sand with some low grit like 120, then do a 200 grit.
i painted my skis black so i just used the primer, did a bunch of layers then did a bunch of layers of clear. do it at a 2 feet distance from your skis its okay if you don't get ever spot on your skis the first time. you still have other coats to add that will make it all come together in the end. its gonna chip along the edges no doubt about that, but the top sheet is whats important and mine has stuck.
then again the madtrix topsheet is a different material, its not the smooth and shiny plastic based like on other skis, so i don't know.