Here is how I built mine. I did it pretty much how I showed you in the diagram...mostly.
Inner ring: I drilled the two holes so that the kevlar would clear the tube once it was in. Then brought them together with heat shrink. Since I got epoxy on my kevlar and couldn't pull the two ends to be more equal length or what not, I just tied a loop in the short end for attaching the chute and let the other end run long (about 18") and it will attach to the main harness.
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Outer ring: I just flattened one side with my belt sander and brought the straps out there. Sealed with epoxy glue. I put #6 weld nuts on the back side and epoxied them in place. My lid/sled will mount via the weld nuts.
View attachment 334436
Other options you can utilize:
1 - Put an eyebolt in the inner ring on one side or both sides to attach you kevlar to. You would still have to run the kevlar through the outer ring.
2 - Put an eyebolt in the outer ring. When you step back and look at it this is the same method used on motor mount assemblies
FWIW. I had #4 wood screws in my inner ring, plenty of material to bite into. I pulled them out for now and will space them out a little neater before going back in with them. You can counter sink some into your outer ring through your shoulder if you feel it is necessary (yeah I know you said you didn't want to). My Cowabunga flies with only the outer ring held with epoxy and screws with the harness attached to it, no inner ring at all.
However you do it , just remember to leave enough material around the tube so you can get a good seal against ejection gases.