So, it's been a while without an update. I've been busy breaking parts

I destroyed a transmission and multiple rear-center driveshafts.
I hope this solves my issue with breaking rear driveshafts...
I started with a set of the new Integy steel center driveshafts. I'm not thrilled about the quality of them, but they are the only metal ones available. My chassis is 40mm longer in the rear than stock, so the driveshaft needed to be extended quite a bit. I first cut the Integy driveshaft in half. Next, I bought some 6061 aluminum tubing that has an inside diameter of 3.9 mm. The Integy driveshafts are 4 mm in diameter, so I drilled the center of the tube out just slightly, so that is would slide over the cut ends of the driveshaft. I made sure the fit was VERY tight. I then used a large vise to press the ends into the tube. At this point, the assembly felt very strong and I think it would have been fine, but I decided to take it a step further to be sure. I drilled a small hole at each end all the way through the tube and center shaft and drove a wheel hex pin through it. Finally, I covered it in heatshrink, just for looks.
What do you think?