Thanks very much for this gtrguy - the creativity and expertise on here is extremely impressive and reassuring. I think your idea here would work and I'd be tempted to try it, though don't have the tools to hand. Finding the materials shouldn't be too difficult, but securing or accessing the right tools may take a little time. As I have no engineering skills, I'd probably need some help here - my sister-in-law has agreed to help in principle, though I'll need her to see the bass for measurements. On the issue of reaming the hole, when I inspected the inside of the cavity, it appears that there's a small metal washer recessed into the wood behind the surface - this would probably make any reaming a little difficult. Finding the right gauge of tubing is going to be critical here. Thanks again, much appreciated.