[prndl]

I don't think it is your surge protector. There is an open neutral somewhere up stream of your converter. Probably in the cable/cable plugs/cable to coach connector.
It's somewhere that was moved or jiggled when you were connecting and disconnecting the surge protector and or shore line.
When you tested the 120V outlets and found 240V was that on just one leg of the outlet or are you adding what you found on each leg?