What you're saying leads me to believe that the water line running to the toilet may branch off of the hot water line. This is not correct but sadly isn't uncommon. I discovered when remodeling one of the bathrooms in my own home that the builder had the water line for the toilet connected to the hot line instead of the cold.
I recommend tracing those water line from the toilet to make sure that it's not connected to the hot side and calling for hot water every time you use it. This would... view full answer...
I'm really sorry to hear about the mishaps on your brand new trailer! When reading through your descriptions the first thing that comes to my mind is the possibility that there's an exposed wire somewhere along the trailer that's making contact with the frame. This is essentially powering the frame so that when you attach the ground cable it's creating those sparks (which is not normal).
If this isn't the exact cause of everything, there's at least something going on with the factory... view full answer...