I've installed a thermostat (same inexpensive water-heater device used by Miss Prissy in hers) in my cooler incubator. Although it works, it allows too much fluctuation in temperature. I have repositioned it to bring the fluctuation down to 7.5 degrees total, but I imagine I want it much tighter than that (i.e. - 1 or 2 degrees total)? Any ideas?