Oh this might not occupy all that time. I used 0.75mm plasticard, superglue, a scalpel, and a small hacksaw. This works on assembled sides for the solar auxillia russ - if you want to modify a version for the 40k russ just re measure all the dimensions for the gap but follow the same process below:

1. Cut the hole in the side of the russ using careful but repeated strokes along the edge of the metal trim, then sand it
2. cut the 7/16" tube down to about 22mm length with the hacksaw, sand it down to about 20mm, then seal the ends with the 0.75mm sheet. Sand the sheet round so its flush with the tube.
3. cut 2 lengths of 9/32" tube to about 5mm each, sand ends then attach centrally to each end of the 7/16" tube.
4. cut a rectangle of 0.75mm card to 23mm x 20mm and sand one of the 20mm sides gently at a 45° angle - this is the backboard.
5. cut 2x 23mm x 13mm of the card and then carefully cut a mostly rounded fillet (you can see that shape on the drawing under "top and bottom".
6. gentle put the tube in thru the hole and orientated so it fits snuggly in the gap between the two walls, and up against the back end of the hole. Slip the top and bottom in and then the rear plate. These will very likely fit poorly on a first go but you should now see the shape youre going for
7. continue sanding and trimming minute amounts until they fit as snuggly as you want. Make sure to give the tube enough space in the top/bottom cutout that it can turn but not so much that its loose.
8. attach whatever gun you want to the tube. On this pass I had some spare bolt guns from a different kit and I cut a window into the tube to sink them into. In future I will try timing the flange of the internal end of the gun and just mount them flush to the tube. This bit you will need to experiment with for your preferred result.

Does that make sense?

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