Make Gas tanks Universal
This suggestion is mainly to improve concepts like Hydrogen based fighters, but also to allow more creative building in other areas:
Make o2 tanks and h2 tanks into a "Gas Tank"
A Gas Tank would be able to take either gas. The block models and components stay the same as before. They get a switch added for which gas you want them to take. This switch can be flipped at any time in the control menu, and the gas left in the tank can still be used even if you are currently filling another gas into it. For example, a Gas tank can be filled with 20% o2 and 80% h2 and thus feed your thrusters as well as your oxygen system.
BEST CASE: Don't make a switch, make a slider for o2/h2 percentages the Gas Tanbk should fill up to