The skunk stripe is the walnut strip down the back of many 'classic' guitar necks. It is an indication of the type of truss rod within: A single steel bar in a curved channel. To create a perpendicular force, a truss rod needs two members: one in tension and one in compression. The skunk stripe rod uses the neck itself as the compression member. This was originated on a guitar neck and then extended to the bass. The problem is, a bass neck is much longer and less stiff than a guitar neck and is under much greater compression. The last thing you want to do is add more compression. Also, using two dissimilar materials for the two members inserts a host of issues, and using steel against wood, that's just hideous. The wonder of the skunk stripe is that most of the time you get away with it, despite how awful the design is. Of course, it is very cheap and easy to manufacture, in a factory setting.