Hi,
We live in Montana and go to Banff and Jasper several times a year.
Its absolutely beautiful - especially the Icefields Parkway, Yoho, Lake Ohara, ... just lots of great places. in my opinion, its the best mountain scenery you can see from a road in the world.
But, the place is usually a zoo.
We would not go there in the summer.
October helps, but there can still be quite a few people.
We like October and we do go without reservations in October and later.
The Tunnel Mountain campgrounds outside of Banff are large and often have space, but no guarantees.
There are some overflow campgrounds that can be a place to go if most everything is filled up.
One is just South of the Lake Louise area. Pretty much a parking lot.
The Icefields Hotel which is at a beautiful spot on the Icefields Parkway has a huge parking lot and its open to camping on the North end. It is literally a parking lot with an outhouse, but we have never seen it fill up. It has a view to die for - I actually like staying there.
If you do Yellowstone this year, its going to be interesting with all the flood recovery. They just reopened the southern part of it today for even number lic plates - odd numbers tomorrow. Sounds like it worked well.
I would strongly recommend if you do Yellowstone that you camp along the Beartooth Highway to the NE of YS, but it might not open at all this year due to the floods. Best mountain scenery in MT.
Good campgrounds and some nice dispersed camping areas.
Not sure, but I'd guess that just showing up at YS in October is not going to work. You might find something outside the park.
A good option in MT when regular campgrounds are running full is the fishing access sites - many have camp spots and some are in great locations.
If you go up to Banff from YS along hwy 89 (better than I15) - there are some nice FS campgrounds on the east slope of the Rockies.
Gary