I believe the stated information is:
1. No continuity neutral-to-ground in the unplugged RV. This is correct.
2. Dead short neutral-to-ground in the shore power outlet. This is correct.
3. ~30 volts AC from the chassis ground to the ground terminal of an AC outlet. This is incorrect and a significant safety hazard. It means the safety ground from the shore power outlet is not connected to the RV chassis as it should be.
The Progressive Dynamics converters are pretty bad with RFI emissions. Your situation sounds worse than what I have observed. Fixing the ground connection (item 3 above) might help with this.