Dunc 18ND W.CO
I used the existing wire from the chassis battery through the coach battery box and associated inline fuse that went to the inverter - I think! This now powers my Victron Orion 12V to 24V lithium battery charger mounted inside the right forward bay where my electronics are all mounted.
I recall the wire channel under the driver seat proved impossible to access for more wires.
Hope this helps.
Dunc, W.CO, 2018 N24D
800W Solar, 10kWh Tesla Coach