The power issue is why a computer makes more sense overall. Computers run on DC anyhow so all you have to do is buy a DC to PC power supply, they are fairly common and not too expensive. Add a 7" touchscreen display which mounts in the stereo area and wireless keyboard/mouse for emergencies. Everything runs from a 12v 30Amp feed including head-unit (to send sound to Amps). Obviously for real gaming you'd want a bigger screen but otherwise it works out very well.
Back to subject - Xbox will have to run from an inverter cause nobody makes a DC to Xbox power supply, yet...
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