When dealing with high energies, the 'belt and braces' approach is more than justified
I would place TVS diodes all over the unit if I thought it were needed, but you have already come up with an excellent robust design.
Sadly my kit is still in its box awaiting its turn on my to-do list.
Off topic but maybe of interest ?
I was demonstrating my Chinese Transformer based battery tab welder to my neighbour at the weekend. My first weld resulted in a loud BANG, from inside the unit and its lights went out. I thought I had blown the fuse but no, it was fine. House power was still on as well. The give-away was the lack of the neon light on the power switch ..... no mains power was getting to it.
A quick look inside revealed no smell of burning or obvious failure. A continuity check proved that the mains power cable Neutral wire was open circuit. Further investigation revealed that the blue insulation on the wire after it entered the units case looked slightly discoloured white in a couple of places. I pulled on the cable and the insulation could be seen to stretch ! I cut open the wires insulation and found just white powder inside at two separate locations. The copper wire had turned to powder ! No signs of heat damage.... the copper was gone. I looked at the cable quality and found that the manufacturer had used really low current cable with very little copper cross sectional area and very fine strands in the insulated wires. I am not certain of the failure mode, be it corrosion or gradual erosion of the fine wires, but it gave up in the end. I am fitting decent quality 13A rated cable to it instead.
Fraser