Well, it is way simpler than hard drive in your computer. The problem is that it is not mass manufactured, and needs a lot of engineering work. (also i'm considering just the brains).

I'm looking at this table for the solid coolants:

http://physics.info/heat-latent/

Frozen ethane looks promising, half the per-kg latent heat of the liquid nitrogen, and it's probably denser. The freons also have very low melting temperatures and may have high latent heat of fusion but I cant find any data.

It's also hard to estimate the rate of heat transfer through multi layered reflector. I'll think it over when I have time. I'm quite rusty on this. For those who want to calculate, the radiation is proportional to temperature to the 4th power (Stefan–Boltzmann law), and in the equilibrium the shield radiates as much as it absorbs, and I dunno how to model shiny metals.

In any case it would be great to just boost maintenance-free time to a couple years. Not sure everyone wants to wake up after event that maintenance was suspended for decades or a century. Anything can happen incl. show trial for some nonsense crimes. edit: or worse yet the copyright expiration on yourself as IP.