I can imagine that the Fenspace version will be much more thermally efficient than the actual real-world version. Besides, you can cut a lot of waste-heat out of the picture by using it to pre-heat the the fuel and pre-intake gasses.
Also, I'm pretty sure these little guys would remain in their own closed environment. Since their intended purpose would be emergency aux power, then you'd want them shielded against vacuum. Of course, that'd also mean you'd want them to be bundled up with a compact atmosphere recycling system, a la Explorers. Heck, you could probably package the whole shebang into an easy-to-apply self-contained circuit card. Plug it into a standard PC slot and the built-in power management hardware/software does the rest.
Also, I'm pretty sure these little guys would remain in their own closed environment. Since their intended purpose would be emergency aux power, then you'd want them shielded against vacuum. Of course, that'd also mean you'd want them to be bundled up with a compact atmosphere recycling system, a la Explorers. Heck, you could probably package the whole shebang into an easy-to-apply self-contained circuit card. Plug it into a standard PC slot and the built-in power management hardware/software does the rest.