Ultrasonic vaporization

I'm trying to fabricate a tank to test the efficiency of an ultrasonic vaporization system. The manufacturer's representative said that the transducers' circuit boards must be mounted onto a heat sink that in turn must be connected to a water-filled metal tank to absorb the heat, otherwise the transducers cannot work. The transducer faces should also be in direct contact with the water for the ultrasound to vaporize the water.

My project engineer suggested the use of a stainless steel tank. I agreed with his idea, but this posed a problem for me. I can use a copper strip as a heat sink and solder it to the tank, but this means that the water within it will get quite hot. Obviously I have to use some sort of sealant to prevent leakage, but what sort of sealant can I use that can withstand the temperature?

According to the transducer manufacturer's rep, the heat generated when the transducer is used can be hot enough to melt the circuit board, and I need to keep 16 such boards cool. I think the temperature produced by each board can be as high as 90 to 100^oC, which means that the water may get as hot as 70 to 80^oC. Can ordinary silicone sealant resist this temperature for more than 1 hour? If not, then can anyone recommend me a more suitable type of sealant instead?

Thanks for your help everyone.