As a sidenote: the "Space Hulk" mod that was being brainstormed earlier... I find the idea fascinating.
I was thinking about it, and decided that supercold space would work. The outer hull would be frozen, and nearby rooms would be cold, but a few reskinned geothermal vents could provide heat to the interior, or some power + heat mapgen structures. You'd end up with warm inner rooms and progressively colder outer rooms. Spacesuits could provide like -2,500 safe temp for the helmet and suit separately and significant movement penalty. Glittertech suits could be skintight and suffer no movement penalty, which could either be suits or be a different 'race' of humans with a further safe temp, which would mean that when killed they wouldn't drop the suit, since they're probably designed for each user specially, then give butcher product for scraps of glittertech skinsuit material.
World map could be interesting too. The biomes could be 'engine' and 'cargo' and 'cryo' and 'command' and such, and have very restrictive mapgen for how things are placed in these areas. Imagine that in the Engine biome, you get bonus power options straight from the drive, but have issues with radiation and raiders/manhunters who seek out the engine's power. Or surviving in the more heavily fortified hallways of Cargo biome, with more secure walls and compartments, but occasionally suffering power outages as things happen on the Engine side off-screen and power goes down for a while. Or in Cargo, you can get events similar to the 'crashing ship' mod, where it shifts cargo along z-axis and causes whole structures to 'drop' into rooms, as if the containers were moving on rails, obliterating things in the spot but moving in hoppers full of stuff.
The biggest thing is making worldgen VERY strict. The map would essentially have to be pre-made by hand. Any random allowances on the walls could result in overlap or gaps which would ruin the ship's structure.