In construction, hemlock is used frequently, but it is notorious for some extreme warping. I suppose it would eventually stabilize, but I remember going to a local lumber yard, to get a 2 x 8 treated hemlock plank. I wanted a 14' plank, and they only had one left-- the middle was on the ground, and both ends were nearly waist-high in the air. Other builders have told me of hemlock studs twisting so aggressively inside a wall that they eventually broke themselves in two, fighting against the restraining wall fasteners.
(It also rots easily, but you aren't going to expose your bass to the weather, I expect...)