Juan: I used to use weight tubes and found that they just did not hold up in my practice arrows. I switched to weed eater line which did not give me that problem. However, after talking to Bob Morrison about increasing arrow weight he suggested the best way to do it was to add the weight to the point. I took his advise and now have arrows that shoot better, penetrate better and I have none of the hassles associated with adding tubes, rope, plastic line or whatever to my shafts.
One other tip, if you go to the weed eater line crimp it every 4-6 inches so that it pushes itself against the inside wall of the shaft. This will eliminate any noise you might get from it rattling around inside the shafts. Adding weight is a good idea, IMO, but, as I said, I have found that the EFOC everyone talks about is really a good thing.