Volts x Amps = Watts (or close enough for our purposes).
If you have low volts, it's going to take more amps. If voltage is low, it tends to draw more amps and overheats. If it's a little, it will cause damage over weeks or months. If it's really bad, it could fry your air/con in seconds.
A transformer helps but as someone else pointed out, it's not a cure all by any stetch. In order to boost the voltage, it needs either more amps on the input side or fewer amps on the output side. Since the air/con needs a certain amount of amps, that means it needs to draw more amps from the campground system.
If the power is so bad that compressors aren't kicking over, it's probably too low for a transformer to help.