The NH Strathspey and Reel Society has a five string bass that used a bit of stainless steel ducting - ysed to carry air out of corrosive areas - as the resonator. The thing stands about six odd feet tall, with a standard peg head and fretboard, all locally made, but has a 3-4' section of rectangular ducting for the resonating part. They man said he made it five string to avoid awkward reaches for a couple of notes.

DAve