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Instead of using wood to attach skis I suggest using square aluminum tube between ski and sled. On inside place 1/8" or 1/4" x1"W flat aluminum bar stock to tighten nuts/bolts against. Aluminum more stable than wood, less maintenance and weight.
but to be a true smitty you would have to be able to come up with a way for your cross beams to interlock in the aluminum instead of having to use a wingnut or what not right?