Fan alone draws very little power, and actually you MIGHT be able to run the full 13,500 AC on 20 amp, but that could be pushing it.
A typical 13,500 AC will run fine on 20amp, but not knowing what you are using for an adapter/dogbone or extension cords, it could be VERY unsafe if there's any components that are not rated for 20amp service. If all your hookups are safe, then you would need to ensure NOTHING but the AC was running in the camper (shut all other breakers off), anything beyond the AC unit could easily push you over 20amp.