One of the bass players with the Strathspey and Reel Society of NH made a five string bass using about 5' of stainless steel ducting, salvaged from an older high school chemistry lab hood, an enclosure power vented to the outside where noxious processes can be done without affecting the others in the lab. When I didcussed it with him he said that he had added the fifth string to make it easier to access sone of the notes without having to go way doen the neck.

Since it is rather heavy he has mounted two small wheels on the bottom so he can trundle it from his vehicle to where ever he is playing and back.

Dave