you might be better to buy a set of snowboard tuning vices. they clamp to the bench with good hold and have a good non-slip gripping surface. they will work well for both skis and boards.
if you want to build your own thing, build two wooden boxes and add some sort of rubber compound to the tops to give you good grip. they don't need to clamp so they are easily removed and can easily accomodate different lengths of skis and boards. for best results, make three boxes so you can put one between your bindings for optimal support
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