Wood snowboard box project?

well, that first one sounds like a 2X12 (wood dimensions are slightly smaller than what they actually are) And for the other part you would be better off using plywood. Don't use OSB or particle board because they won't hold up as well when wet. Plywood comes in 4X8 sheets you could get a 1 inch thick one, cut it in half and glue it together. Now, by the sound of it, this is going to be one heavy box, heavier than it really needs to be, perhaps you should consult someone you know who has some carpentry skills to refine your design.