First understand that I'm speaking hypothetically here - I'm not seriously considering building up an offboard charger for touring. At least for now.
I would need to add some type of tap for the main battery bus to attach an offboard charger. Custom work, there isn't a standard way to hook up a random offboard charger.
Zero does support hooking up one (or three) additional offboard Delta-Q QuiQ chargers for a total nominal charging power of 2 kW (or 4 kW). It should be possible to wire them all up to charge on a single standard 220v plug. Create pigtails for different 220v plugs.
The onboard Delta-Q draws 8-8.5 amps on 110v. Four Delta-Q's slaved together should draw 16-17A on 220v. (3-3.4 kW charging power)
If I was using something besides the Delta-Q QuiQ for an offboard charger (something like an
Elcon PFC 4000 perhaps?), then I would need to make a custom tap for the battery bus (and likely install a switch for the onboard charger).