Keep in mind that the same horrible issues with inverters in trailers also apply to inverters in trucks. Everything is fine if the alternator is going fast enough to keep up with it. Running it off only the battery *will* flatten the battery pretty fast (70 AH battery -> 35 AH at ~ 35 to 40 amps is 1 hour).
If you can go straight from 12V
to your device, that's a *much* better way to do it. 12V
to USB adapters with DC/DC converters in them are < $20 on Amazon. They will beat a 12V -> inverter -> wall wart -> device setup any day of the week. With a good converter in them, they will be up in the 80 to 90% efficiency range. The older "linear" 12V to USB adapters clocked in at about 40%. An inverter setup might be < 5% on a 0.5 A USB load.