We stayed in St Mary Campground last couple days August last year, and had no problem with heat issues, opening windows for cross breeze. There is a no generator use loop that we were in but there are other loops I believe that have restricted times usage of generator.
To be very Frank the couple of nights we were there we only spent any time in the RV late at night prepping for bed after a long day being out and about and first thing in the morning packing up lunches and drinks to head out again. Walked comfortably to the Visitor Centre to pick up the complimentary Going to the Sun Road Shuttle. Wonderful to be able to concentrate on the scenery and not driving the actual road for a change.
Whenever we return we will for sure book into this CG again, loved it and had many bear visitors and sightings whilst we were there. Many referenced a grizzly but we didn't see the most distinct hump and other signs on it for grizzlies even with binoculars as it started to head down the hill towards the loops with all the berries in (we retreated before he made it all the way down LOL!) so think it was a substantially oversized black bear. Rangers were very on top and active due to the bear activity and we were thrilled to have seen many of these wonderful creatures in their wild natural habitat.
If you are that concerned about having electric, can you maybe rent a generator for your short stay to enjoy the location to it's fullest? Seriously Glacier really needs to be enjoyed from within if you can.
Just my humble opinion for what it's worth.
