Thanks Rob but I think you're giving me too much credit. I'm just making it up as I go.
Side Window Framing continued:
Next job is to cover the panel with the blue velour fabric I bought from Sportsmobile. This one will be more difficult from the other panels because of the window opening. I sacrificed a section of fabric working out how to do the opening.

Probably the best way to do this would involve a sewing machine and some skills I don't have. Instead I did it this way. Cover each of the inside corners with cloth and glue down.

To get the cloth to lie flat on the inside corner there has to be several radial cuts.

Glue down the fabric making sure there are no wrinkles.

Cut around the window opening leaving 2" - 3" of border. Make three cuts at each corner. Don't cut too far in.

Glue and tape the straight sections of the window opening. Use the tape to pull the cloth so there are no wrinkles.

Carefully glue and tape each of the inside corner wedges. Don't get any contact cement on the visible parts. Again use the tape to pull cloth tight.

Wait a day for the contact cement to dry then remove all tape. Everything was secure. I'm not 100% happy with this method but it does work. The cuts in the corners blend in with the previously attached cloth to where you don't see them unless you look for them.

Looking ahead a bit, I've used cut out panels of Reflectix as window shades before want to try something different. To attach my new style shades to this window I'm going to use magnets embedded in the panel. For this to work very strong magnets are needed. I happen to have a source close at hand.
If you're like me, and I'm sure you are, there are a bunch of old computer hard drives just laying around.

If you disassemble those drives, among the various parts you'll find metal platters and very strong rare earth magnets.

Each drive will have a pair of magnets mounted within brackets like these. Size and shape will depend upon the drive model and manufacturer.

Carefully pry the magnets from the brackets. Here is an example of how strong they are.
The only thing holding them in place on each side of my fingers is magnetic attraction.

Don't let your fingers get in the way if a pair start to snap together. It will hurt.
Take four of the magnets. One for each corner. If the magnets in this picture weren't attached to the metal table they would flying towards each other.
On the back of the panel cut away a small square of foam insulation to expose the back of the fiberboard. Glue the magnet to the fiberboard then plug the hole with the trimmed down piece of foam that was removed.
That's the end of the prep work for the window panel. Screw it into place in the van.
To cover up the screw heads I ordered some sample colored caps from a company called Pro-Dec Products.
Color #146 seems to be the closest.
Here's how it looks with the colored caps installed.
That finishes the work on the window panel. I still have to re-epoxy the anchor square tube when warm weather arrives. Like I wrote before I'm not 100% happy with the panel and may redo it sometime. It will do for now.