Don't fiddle with low-temp process until you know what you're doing.
There are a number of water jacket temperature controlled processors on the cheap side compared with jobo equipment. Nova did some for patterson tanks, AFAIK.
If you decide to go with the tub setup [nothing wrong with it] do yourself a favour; buy a calibrated thermometer for such temperatures (true readings are important), and a decent thermostatized heather. Nova had one [novatronic] which althought seems expensive compared with a fish tank one, does its job with enough accuracy for photo processes without headaches out of the box, being somewhat thoughter than fish ones; also, price isn't over the roof. Given current prices of film and chemicals, I find those justified.