OOB Modding without cheating

[Starmyth]

That is what I meant. An external munitions carrier of some type would have the ammunition close. Likely it would then be too close. The carrier could be untowed for actual combat.
Cramped space would definitely be a problem if the additional ammunition was inside the tank. I don't have any idea what tank HE and AP rounds weigh. Of course, larger rounds would be heavier.