> very low density (relatively speaking to today) make them more robust against gamma-rays and other radiation problems once outside the atmosphere?

Yes. Large size transistors (and other IC components) are less impacted by the radiation problems that exist outside the relative security of the atmosphere. Most radiation hardened IC circuity is many process sizes larger than whatever the current state of the art tiny process sizes happen to be at any given time.

But note I said "less impacted". Given sufficient radiation, things will have issues, which is why items like the Shuttle carried the redundant computers, to cover for the possible lucky-strike impacts.