RE: phoenix decathlon
The wing joiner tube is aluminum in the Phoenix model. I believe it even has two in there, the big one spanning half of each wing so I think it would take the stress. Could you make a hatch in one wing on the under side and use blind nuts and nylon bolts to hold it together ? Ben has semi retired his Decathlon. He enjoyed flying it for alomst a year without any mishaps at all, but says that is the only plane that made him sweat every take off and landing. He robbed the radio gear out of it to put in an Edge 540, so the Decathlon is just "hanging" out at the shop these days[&o]