IIRC during transit you'd want as much mass between you and the Sun (as shielding), and as small of a cross section facing the Sun. Probably also to reduce heat reaching the propellants.

So in a cylindrical ship you'd want to have one end pointing at the Sun most of the trip. This is, of course, very different in effect on the hull compared to the repeated expansion and contraction of heating cycles.

There'a maneuver called a "BBQ roll" where you basically set the craft to doing a barrel roll in order to prevent any one side from overheating. I image that could help some.

That's not necessarily true. Even spaceships in LEO will perform temperature-driven rolls so as to distribute heat and radiation. I have to assume that long-term ships like interplanetary transport will do the same.

Of course you can, but "needs to survive 26+ years" was very likely not part of the original design goals. The designers of the time probably wouldn't have expected the dysfunction to be so deep that 26 years later, only the Chinese can seem to stick to a plan.

You can design around a lot of stuff but what you encounter in orbit will ultimately laugh at that bandage and eat it away. AtOx, hard UV, and radiation levels you don't get on Earth just have their way with everything in orbit over time.

You don't get the AtOx going to mars but you have everything else which will utterly take its toll on a traveling craft.