Some new hotkey on Geoscape that opens an overview how much Zrbite and sub ammo you have on all 8 bases.
You can then use this screen to easily order transfers:
Right click Zrbite, and enter a number with numpad and enter, and game will make sure all bases with less than that number will get transferred to from rich bases.
You can also left click base number (source), then another (destination), then item to transfer, then enter number with numpad and enter. The tranfer cost need not be confirmed, it shows somewhere.
I have modded my Sonic Ox to have range 30 km or you don't need sub ammo of course. Still useful for the zrbite.