I doubt that the TV USB outlet will be suitably rated. Likely limited to 0.5 or 1A.
You could consider running the MiBox from the original power supply from the same inverter. I would.
That would be very easy and guaranteed to work perfectly.
Mitsi Fuso CI Ultimate 6.8m 3.9 T/D. 180l fresh/grey. Single 300Ah LiFePO4 for truck/house.
800W solar. Victron 50A MPPT. 6kW Webasto diesel water/air heater.
255l Samsung 230VAC digital inverter fridge/freezer.Gas cooking/oven.