I have thought that if I were to do this again on a plane that was not already skinned, that I would make a space for the tube to pass through the stringers, but would put a doubler at the place where I drilled the hole. In that case, I would think that you could use any material you wish for a conduit. Another thing that I think you could do is to skin the inside after you put in the conduit. I don't see how it could be much stronger being skinned on the outside and inside. I think that the steel being used for a conduit doesn't buy you anything but weight.
"There is a time for building and a time for flying, and the time for building has long since expired." See N64KR at http://KR-Builder.org - Then click on the pics Daniel R. Heath - Columbia, SC See you in Mt. Vernon - 2004 - KR Gathering
