To answer your last question first; No, the 12-Volt system in your Rv should not cause your Main Breaker to kick Off. Your 12-Volt system is powered by your COACH batteries and they are in turn charged by your Converter which operates on 110-VAC. So normally, if there was a problem with the Converter it would kick Off the one breaker that powers it, and not the Main.
Now, your problem with your Shore Power indicates to me that you most likely have a Grounding problem. Considering you have been hooked up and not traveled for 2-years, this tells me that you may have a problem with Corrosion or Oxidation.
Over time, if you are not traveling and "shaking" things around, thus getting a rub at your contact points, you will have these corrosion/oxidation problems occur. So, check your external power cable contacts for any buildup and clean them back to shiny metal.
Then you might have to check the contact points on the inside of your external power connector to your chassis.