The Peltier assembly looked like this while I was epoxying everything together with JB Weld:
The aluminum-case resistor held the heatsink at 105 °F to encourage the epoxy to cure in a finite amount of time.
The 40 mm square block is a squared-up piece of 1/2 inch aluminum plate (manual CNC on the Sherline, nothing fancy) with a pair of 6-32 tapped holes for the screws that will hold TO-220 transistors or the yet-to-be-built TO-92 adapter. The CPU heatsink got a pair of symmetric holes for the posts holding it to the acrylic base, but other than that it’s perfectly stock.
Then epoxy the thermistor brick to the middle of the block between the two screws, stick on some obligatory Kapton tape to prevent embarrassing short circuits, and add a foam collar around the Peltier module to insulate the block from the heatsink:
A square foam shako covers everything, held down with a random chunk o’ weighty stuff, to insulate the whole affair from the world at large.