Has anybody had any luck using ONLY carbon rods or strips. I built one 4 string using 2)1/4" carbon rods with no truss rods, the neck bowed just a touch. I then built a 5 string with 3) 1/4" rods, again with no truss rods, the neck has stayed straight. I am now using 2) 3/16" rods and a two way truss rod. Whats you take on carbon rods?