I'm not seeing a question here. It's not uncommon to find voltage variations at campgrounds - especially older ones. What SoundGuy is talking about is an EMS that will take your rig off-line if the voltage become low enough (or high enough) to damage appliances such as ACs, refrigerators, microwaves, TVs, etc. We have a 50-amp hardwired EMS in our RV and I wouldn't be caught without it. It has saved us thousands of dollars in damage over the last three years of full-timing.
That said, 100V is OK as long as it doesn't go any lower under a load.
Rob