You could run one 30amp relay controlled off the CanBus to power the lights and that box and never worry about enough power to the headlamp ballasts. Let the CanBus control the relay and you'll have the delayed timeout too.
Would it be possible to hook a relay to the light circuit for control and use a 30 amp relay to the HID ballasts ?
I hate using an under rated control device. Time will tell when your feed wire melts