Fuel tank options

[Linkageless]

I'm likely not the first person to suggest this, even in connection to KSP2...  Please can you build some versatility into the fuel tank designs.

Instead of a limited selection of choices, I would rather see the tank shapes as standard structural elements that you can then outfit with the tank types/proportions/capacities of your choice.  I would like to be able to say take a mk3 shell, and outfit it with tanks inside to contain say 300 units of methane, 200 units oxygen, and 100 hydrogen, and perhaps 50 units of empty unfitted space.  This might then be saved as a custom part or assembly, for later use.

It might even be possible to fit out internal tanks to be capable of storing more than one fuel at different times.  Say you have a oxygen tank that is also fitted out for methane plumbing, when the oxygen is all used up or vented, you can then fill it with methane, then later empty it and fill it with oxygen again.

I'm pretty sure there's mods along these lines in KSP1, but wouldn't it be nice if this were a stock feature now we have a more diverse set of fuel choices?

[GoatBOT]

I would also like to suggest that wings be usable as a fuel storage option.  Would be great if the wings were able to hold fuel.  This could be added to work with the procedural wings to where max allowed fuel would be a fixed percentage of internal wing volume minus the percentage of the wing the control surface is taking up.  That way its realistically usable and not OP.  This may require the ability to switch fuel types depending on the intended aircraft being atmospheric or spaceplane.