I've been working on a new fresnel mount, too.
I wanted something sturdy but lightweight enough to hang off the monitor's face.

- It all started with a couple of pieces of 1" thick, plastic/fiberglass honeycomb panel, to make the front and back plates. (They came from a shipping box, for some machine parts.)
- They were gapped and tied together with the four 3/4" square rods of extruded aluminum.
- Their cut-outs were lined with aluminum L-stock, to clean up the edges.
- The inner walls were .032" aluminum sheet metal, riveted together and then lined with black "flocked" paper, to eliminate stray light.
- The lens was held in with small aluminum strips, screwed to the L-stock.
- The TrackIR mounting legs were removed and it was hard mounted to the face.
- On the back of the rear plate, the cut-out was trimmed with foam rubber strips, to fill the gap and cushion it, from the monitor's face.
- Removeable nylon/velcro straps hold it in position.

The final result was very light weight and it holds the lens flat and square!
All that remains is to tie the edges of the front faceplate into the enclosure....eventually!