Most likely I could find a tube to nest inside the 0.5" OD tube. The only problem with that is the fact that the TI rods already fill the inside of the tube. Trying to get the rods into a smaller OD (and hence ID) AL tube that would fit inside the 0.5" OD tube, just will not work. The rods fill the inside of the 0.5" OD tube as it is. One reason for this is that I bent the rods approximately 3/16" from one end about 30 to 40 degrees. I did this so that one end of the rods would not slide through the AL tube. I found that trying to get all of the rods through one tube and then get them through the second tube takes patience and a lot of it as they tend to slide out of the first tube while working on the second tube. By bending one end of the rods, I don't have to worry about the rods sliding out of the first tube while getting them into the second tube. Hence setup is much, much quicker by this simple expedient. Now I understand why the Grilliput grill slots the rods into their tubes instead of sliding them through. Much simpler. Requires a lot more extensive machining though. If you look at the Grilliput specs, they use one tube with almost a 1" OD. They needed to do that so that the second, smaller tube that fits inside the larger tube, is also large enough for the rods to fit inside that tube. To get nesting tubes, I would have to do as Grilliput does and use a tube of probably about 0.85" OD. Then things start getting bigger and heavier. I think it better to just use the two 0.5" tubes and strap them together. Adds slightly to the bulk, but only slightly and keeps the weight down.
It would seem that there are some options here:
1. Do as Grilliput does and use a larger and smaller tube and retain the grill size. This option increase weight for a given grill size.
2. Do as in option 1, but decrease grill size. This cuts the weight since you are using fewer rods and can maybe use smaller OD tubes. What size grill do you need? I arbitrarily decided on 12" x 12" since the BPL rods are 24" and yield 12" when cut in half. Now that I have the grill in hand, I think that size ia about right for me and I would not want to decrease size.
3.Retain grill size and use 2 tubes of equal OD and strap together or just place in pack where convenient and not even bother with strapping them together. For given grill size, this option is lighter than either 1. or 2.
I have decided to use high temperature (tops out at 600F I believe) silicone rubber end caps. They are light, seal the ends of the tubes to capture the rods and are less expensive and lighter than AL end caps. Also, with the high temperature rating I may not have to remove while using and hence reduce the risk of losing the end caps. To practically eliminate the risk of loss, AL end caps would be best, but again heavier and more expensive. Also I'm not too sure that AL end caps would work since threading the thin wall AL tubes may not be practical.