Ox-IA Converter Mod is an useful mod and i think you will need it.
This Mod is a small converter which take oxydizer and generate IntakeAir resource by using some weird chemical and/or nuclear processes. It allows to use air breathing engines in space or on oxygen-less bodies.
But you may have never notice it IntakeAir is very heavy, heavier than Oxydizer, mostly because air intakes hold only 0.2 to 0.5 at most IntakeAir. So, it has been modified to convert the Oxydizer into IntakeAir on demand.
Test it and leave some feedbacks.