So, it seemed the easiest way to start, was to measure the Bergens internal dimensions, and then cut a back panel from sheet metal to these, and see how it fit.
If youve ever tried to measure the inside dimensions of a bag, you'll know how hard it is to decide what the actual numbers are! But, I had some figures, and I had a nice clean sheet of galvanised steel (the top cover off of an old video encoder)
Clearly my hacksaw was no use for cutting the long sides! So, most of the work was done using the nibbler. These are great tools, and with care can get right up to the mark and do a reasonably straight cut, reducing the amount of filing needed. The downside is they can be hard work on the hands
As shown above, the panel is almost in shape, with the reduced size end (where the battery would be) to allow the battery strap to be used to secure it.
As i'd cut this from an equipment rack, this left me with a nice 50mm side, which helped see how the frame would fit. Unfortunately, as can be seen by the above photo, at these dimensions it was a little too big. It would have fit at a push, but the corners would have worn through the fabric eventually.
So the side had to go and 10mm be taken off each side. I could have just done one cut and removed 20mm from one side, but although that would have reduced the pain and blistering, it would have displaced the lower section. So two cuts it was. I also increased the lower section depth by another 5mm to give some clearance to the battery strap. On the above photo this has all been done, but you can see that the bottom edge still needs more off.
And then the final sized back plate. 10mm off the bottom edge. Ive put my DX-70TH on it as an example of the idea, and it fits - heatsink to end of tuning knob - just within the diameter of the frame.
One task remains at this stage - a slot needs to be machined about 2/3 of the way down (roughly where the right hand side of the radio is) to allow for the passage of the main strap.