As far as material for the tube, density is important....but to a point. As you could always seal the inside of the call. This is where the resonating effect remains the most important aspect of the call. So, material choices is not as important when it comes to the tube body itself, just remember to keep the inside sealed as well as possible. Now wall thickness, I have seen tubes made from plastic with wall thickness near 1/8th of an inch, the metallic snuff can calls had a wall thickness of less the 1/16th of an inch, both calls made great turkey sounds, when it comes to wooden tubes, you can go as thin as you feel comfortable with when turning the call on your lathe. Sound wise, well that is a whole new game, I suppose if you got thin enough you create a vibrato problem, who knows, I would not concern myself with wall thickness other then for turning reasons.