Scuttle fuel tank repairer request.

[Colin Wilks]

Given the very small size of the holes causing the leaks, and the difficulty of getting everything to a useful temperature for soldering without a fireball, have you considered using a copper patch, but sticking it in place with epoxy resin?
Many epoxy resins reckon to be unaffected by petrol.
You already have a very nice clean, slightly rough and presumably grease free surface on your tank, so halfway there.