I've ordered some thermal paste (should show up at the 40m on Wednesday) for the thermistors and 2 silicone heaters for the panels. The silicone heaters are from McMaster (picked by Megan) and should allow us to deliver ~15 W of heat to the panels if we wire them in series.
The heat capacity of Aluminum is ~0.9 J/g/K or 45000 J/K for a 50 kg chunk. With no heat loss, that means it ought to take (45e4 J)/(15 J/s) ~ 9 hours to heat up the whole thing. Which is OK for maintaining the temperature, but pretty painful from the standpoint of initial warm up.
Perhaps we ought to just use the power supply we used for the reference cavity heaters. That one is too noisy for any kind of precision measurement, but ought to let us test the time constants of the box.