I found this on the net, where someone started with a simple beaker and then also created the successor with a gastronorm container:

http://www.ibrtses.com/g/dampfphasenloeten.html (in german)

The interesting bit is how he did the heating: immersed power resistors, rated for 5 W. Apparently he did some tests and came to the conclusion that even 30 W per immersed resistor is acceptable. Resistors are rated for a specific dissipation in air, but those numbers don't apply when the resistor is surrounded by a fluid with hugely different properties.

However, supplying power to immersed resistors might be a problem. Using 230 V just doesn't feel right even if the Galden doesn't conduct current, because it's still a steel container (afraid of shorts...) and the cables would have to exit through the top where I'd be handling the PCBs.

About 10 rows with 4 or 5 resistors each fit into the available space at the bottom. At, say, 10 W each that's a total power of 400 to 500 W. This could be handled by a decent ATX power supply, or a 24 V PSU for less current. That's an attractive option epseciall with PWM, but with the drawback that I'd need enough Galden to cover the resistors.

Power resistors aren't cheap if bought from digikey or mouser: about € 0,50 to 1,00 each. That's a lot if you need 50 of them. Replacing one would also be tedious.

Regarding heat transfer, immersed resistors might be very effective since they provide a relatively large surface and there's no extra heat loss from an external heater below the container.