Ok I have an idea.. SEE Photo.

I've looked and considered many metal and plastic 'eye' type connectors. Nothing really jumped out at me as obvious/ good for the purpose.
Entre some more sewing.

Simple 50mm binding webbing (Thin), or could use thicker webbing. Folded and stitched enough to locate the tent pole end.

I plan to sew this onto the stem stitch on the ledges base. I'll post more when I have done so...

Doug G, has put together a great video of the frame build:

https://youtu.be/kJcZ5XrqhbE

Good stuff!

This should also go in the portaledge open source /DIY section of the forum, here:
http://bigwallsforum.com/index.php/board,5.0.html

Very very interesting!! Thanks Deuce!

We completed our trapezium homebuild in time for the Big Canopy Campout on Oct 17-18, was sewing up til midnight the night before and was so happy to be able to rig the trapezium 40m up a tree in a beautiful big Eucalyptus regnans surrounded by patches of rainforest and a flowing river!

Thanks so much Deuce for all the support and for the kit and fly fabric! I just followed the instructions in the trapezium design notebook for the fly and it fit perfectly: https://bigwallgear.com/d4-trapezium-design-notebook.html

We decided to sew the front seam because it turns out waterproof zips are extremely hard to find in COVID times with delayed or impossible overseas post. I've left it so it's possible to unpick and add a zip if we do get one. This necessitated a drawcord on the bottom which has worked alright but is difficult to adjust from inside the sit so I might have to make some adjustments.

The plan now is to order a roll of fly fabric from Ripstop by the Roll and when it does arrive make some more flies for the DIY ledge and other kits Deuce has kindly donated to us for tree use.

Here's a few pics of the fly!