The National Park sites have electricity for sure, and do not have sewer, but I can't remember if they had water, or we had to fill our tank. We stayed in Lake Louise, and went as far north as the icefields, and as far south as Banff. Then we took the coach to Jasper since we headed to Edmonton from there. It is about 150 miles, and good road, but there is so much to see along the way that I would strongly recommend you do take your RV. Although the road follows the Rocky Mountains, it goes along the path of a river valley for much of the distance. As I recall, there is only one significant climb, but it has a turn off/look over and it was no problem.
August & early September should be ok, but remember you are at high elevation, so you never can count foul weather out. But check the campground websites for when they close since most are heavily staffed by University students who head back to class. I just checked Parks Canada website, it looks like they close down Sept 14, here is the link: https://reservation.pc.gc.ca/Banff-LakeLouise?Calendar, but the town of Jasper is just outside the park, so there are private campgrounds, here is the Good Sam link of parks: http://www.woodalls.com/Campground/Default.aspx?city=jasper&zip=&state=AB&country=CAN&name=&goodsam=0
Ed
