Custom built aluminium/wood upright that I play in The Memphis Morticians. (I've gotten positive reaction regarding the sound from several much better players than myself). It was made out of .060 aluminium. I made a negative of the shape in MDF (like dense particle board). Screwed the flat sheet to the form then went at it! The back was the same. I made a "steam box" to bend the 1/8" maple sides (box w/ hole in it and radiator hose attatched to a Kettle). These pieces were glued to a hardwood skeleton frame.
You can read more about this bass on the message board.