Assuming all campground sites are 30 amp service for the purpose of discussion.
Argument in favor of "not stealing": Every rig is entitled to draw 30 amps, enforced by the pedestal breaker, at whatever voltage is available. With the autoformer, you have chosen to have fewer amps at a higher voltage available to your devices. At the pedestal you're still limited to 30 amps at whatever voltage is available. Same as everybody else.
Argument in favor of "stealing": Because of low voltage, every rig will draw fewer amps that they would if the voltage were higher. With the autoformer you've created an unfair advantage for yourself compared to the other campers, and you're drawing more amps than you would without the autoformer.
If you chose the stealing argument, then you have to say that somebody who runs their water heater or fridge on electric is also stealing from those who run it on propane, or somebody who chooses to run the air conditioner is stealing from somebody who doesn't. All IMO of course.