More Ammo???

I have all the ships now. And all of them have internal cargo space. Apparently I can put extra ammo in this. I just dont know how. Any suggestions please, because Im seriously stuck .

You need to trade for an internal magazine. If you have all the ships, you should have a trade for it (or be real near to the time when you will have a trade for it).

If you do have one, you can open the customized loadout screen and select a missile launcher. It should have a radio button labeled internal magazine you can click to activate.

The internal cargo space is also taken up by assault cannons.