im beginning designing a 6 string bass neck (fretless) for a custom bass im building, and i was just wondering, if it would necessary for a dual truss rod along with carbon fiber rods (which im sure im going to be putting in), any help would be great

1

he speeks da troof.

You don't need 2. Truss rods are for adjusting more than for strength, and as you said, you're putting CF rods for strength. Unless you plan on having to correct a twist in this neck, you don't need 2 rods.

Using hard/dense woods in the neck, 1 is fine, and no need for carbon fiber IMHO. Once again if you're using good woods you'll hardly ever need to touch that one rod. At least that's my experience.
Good luck!
Dirk

thanks for your help guys! one truss rod it is!