Reverse chuck as shown in the picture is the way to go. We use "Air-Flex" for the inside duals now which work great. There is no pressure IN the extension so if it breaks, no flat.
We have tried several angled extensions for the outer wheel, but they turn too easy and get loose. They are pressurized, so when that happens....flat tire. You need to either monitor them very closely, or use no extension and a reverse chuck as shown.
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