It's easy to under-tighten the t-bolt clamps because the nylon lock-nut provides resistance when tightening, making it seem like they are tighter than they are. If your elbow is popping-out of the coupler, make sure the clamp is not seated right on top of the bead-roll. This is probably the most common installation mistake and it will cause issues no matter the tightness of the clamp. Also, as has been mentioned, make sure you clean any oil residue off all surfaces of the elbow, coupler and clamps themselves. As always, if you have any issues, don't hesitate to get in touch.
I just quickly slapped a kit together, here are (bad quality) photos showing how everything is intended to fit together. As you can see, the components fit together tightly, the adapter is basically seated in the elbow. Push both the adapter and the elbow in as far as they will go, ensuring they are seated fully inside the coupler. This allows for the clamps to sit fully behind the bead-rolled edge while using the full "contact patch" if you will. If your installation doesn't look like this, it should.
And sorry for hi-jacking the thread, enjoy your road trip!
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