Cosmo-K 10 is right about the working properties of beech. Back when the common man's furniture was all wood, most chair spindles were beech. It is rare to find anything made of beech lumber such as table tops, dressers, desks, etc because the lumber warps and twists. If your bed wood is to be 5-7 inches wide, you will have to bolt it down pretty well to keep it flat. Beech is not at all durable, though. Its rot resistance is similar to maple, a little better than birch. I agree that black walnut shouldn't be used for truck beds. Even pallett grade walnut can make a lot of pistol grips and candle holders. Walnut isn't durable either, and it is softer than beech.
Go for the gusto, and use black locust. Very pretty yellow color, and far more durable than oak or southern pine.
