Lots of good info especially the boondockers, booked a KOA 30 mins away at Quechee/Pine Valley. Stoked!This looks like the closest to Killington with water/elec. http://www.irocamp.com/index.html
I've found most of VT state parks don't have water/elec. You could also look on https://www.hipcamp.com and https://www.boondockerswelcome.com. Basically people offering an RV site on their private property.