It was the breaker at the campground when I had to use a site that only had 30 amp service. I then moved to a site that had 50 amp service, then everything worked. this happened 3 times. it was never the breaker in the m/h, it was always the breaker on the c/g post. I am sure the block heater was not turned on. I would assume that the cord hanging in the eng compartment had to be plugged in for the block heater to work. when the tech removed the wires from my breaker on the m/h, I could use 30 amp GFI breaker without it kicking out.
I'm sorry I didn't explain all of this in the beginning. I was trying to keep this brief and still get some input.
The tech talked as if the problem laid in the GFI circuit. the way I understood him was that most C/G used GFI only on 30 amp service. He said that GFI isn't needed on 50 amp connection.