OK, let's follow the fault.
1. You have voltage from the hot to ground. That means that the hot (black) line is good to where your are testing.
2. You have no voltage DIFFERENCE between the black and white. I suspect that the neutral circuit has been broken somewhere and some LOAD attached beyond the point of the break is feeding "HOT" back to the neutral wire.
Please do this test just to confirm what you have already stated:
Do you have 120 volts between the ground and BOTH the black and white wire?
If so, try this:
Monitor the ground to neutral voltage and switch off one circuit breaker at a time. By this I mean start at one end of the line of breakers and turn one off, then check the G-N voltage. If it still exists, leave that breaker off and then turn the next breaker off also. At some point, I suspect that you will have the G-N voltage drop to zero. That will confirm my idea from point 2 above.
The most likely cause of an open circuit on either the neutral or hot is the "Back Stab" connections at an outlet. They happen much more often in RV use that in home use because of the vibration caused by road travel.
2015 T12RBST Flagstaff Hardside
2008 Itasca Meridian 37H