Nice to have the tools and skills Brent - looks like a very nice job
I'm not sure you need worry about thermal stability too much. Peltiers seem to do OK by feeding just the right amount of power for the temperature, analog or digital control. The mass of a 1.2mm coldfinger, as used in the Canon's you've no doubt seen on the forum, is adequate to hold temperature for several seconds once power is removed. I find my system very responsive and accurate +/-0.3C, most of which is the digital switching effect on analog sensor readouts.