Well I have decided to build one after a lot if discussion.
The tank is a 2.5 litre small food container which is tall and flat and thin with a removable lid.
I have placed a 50w salt water aquarium heater in it that will warm water adjustably to nearly 40 degrees from the cold tap in less than 10 minutes, which should be fine as I intend using freshly made etch which will be pretty warm to start with, or pre-heated by placing the tank next to a radiator in the study.
I have a small aquarium aerator and an air stone, that will provide the bubbles. If needed I will add a circulation pump.
A small thermocouple and LCD readout (+5V) from a PC will allow me to monitor temperature.
To reduce the volume in the tank I will use a sealed 'hippo' made from thick plastic wrapped around a piece of wood and then heat sealed.
A count up and cout down timer will be added to the assembly.
PCB will be suspended from the lid.
Images to follow.