Evaporator coil

[seanf]

Unfortunately I cannot mount the pot normally withe the opening on the top, so the first solution you proposed is not feasible,

Could you drill a hole in the side of the exturnal pot, and once youve got the internal pot and its coil inside the exturnal pot, seal the gap. The gap between the pots wouldnt be pressurised so shouldnt be to tricky to seal. Then turn the completed assembly and fill it with a fluid?

also for the second suggestion, I don't have enough skill to build something like this, but it does sound really nice

Could you use a local engineering company to make the pot? have them fit stubs onto the outside so that you can braze copper tube onto them.