You obviously had a resistive path from the water heater element back to the ground at the campground service panel. We know it was resistive because if it was a dead short or the resistance was low enough the current would have been high enough to trip a breaker. What we're not sure of is where the resistance was. But since you had a hot skin condition we can presume that a significant part of it was between the frame of the trailer and the campground panel. 

The heater element is supposed to be about 10 ohms so if there was say 10 ohms resistance or more in the grounding conductors then there would have been a "normal" 12A or so current flowing in that circuit which would explain why a breaker didn't trip. As the article says you want the whole ground path back to the camp panel to be about an ohm or so in order to trip a breaker. The high resistance could have been in the campground's system I guess.   What resistance did you see between the trailer ground pin and the frame? 

@offgrid - I know that makes perfect electrical sense....but on your advice on my previous thread I checked my ground connection (at both the electrical box in the trailer as well as from various AC outlet ground plugs) to various chassis points and they all show little to no resistance.  So, I'm still confused on this myself in regards to my issue....it's been so rainy here I don't want to be crawling in the dirt under the trailer but I'm still pondering the "why" it happened.

There should be a ground wire tying the ground pin from the power inlet to the trailer frame. If that ground was  there you shouldn't have gotten shocked by the short at the water heater element.  Just fixing the water heater doesn't fix the grounding problem, so you can get shocked again in future if you get another short somewhere in the trailer electrical system. 

Heating element...and thermostat was blown, and now the AC power switch needs to be replaced...but no more issues...

Have the guys drain the water heater and unscrew the heating element, pull it out, look it over. Same with the anode rod.

Sounds like there are two problems. First, the water heater element is shorted to the chassis of the trailer. This is not a solid short, it is what is called a resistive ground fault, meaning that it is leaking a small current to the frame. That doesn't mean its not dangerous, even a small current can kill you under the right circumstances. That's what GFCI's are there to protect against. They are generally set to trip when they see a ground fault fault current of only around 6 milliamps. 

 You have got rid of that fault current for now by shutting off the breaker to the water heater. Don't turn that back on until you have fixed it, in the meantime just run the water heater on propane.

The second problem is that you look like you are missing a ground connection to your trailer frame. If that connection was there then there shouldn't have been a noticeable voltage on the door frame.

The trailer frame is not directly connected to earth ground of course. It is supposed to be connected back to the RV panel and from there back to the campground or home distribution panel and from there to a ground rod.  So an open ground could be either be on the trailer side or the campground side. Get an RV EMS and use it to check the park electrical system prior to connecting to it. It will detect an open ground on the campground side  if there is one. Use it every time you connect to grid power. 

If the power coming in checks out OK then there is most likely an open ground between the RV panel and the frame. Ask you brother in law to look for that and repair it. He can confirm its there or not by pulling the trailer power connector and measuring the resistance with a multimeter between the ground pin on the trailer power inlet and the trailer frame. Or, you can buy one yourselves and keep it in your RV toolkit, its handy for lots of things.