Just had another thought, rare for me!
Instead of taking Hwy 40 to Peter Lougheed, take HWy 3 West. Stop at the Frank Slide interpretive centre then overnight at Fort Steele (Commercial RV park here and the restored fort is across the Hwy and worth a half day).
Go back to Cranbrook (Interesting railway museum here if you like old trains) and then to Kimberley. Overnight at the Riverside RV park/campground then visit the underground mining/railway museum in Kimberley.
Drive north on Hwy 95 to overnight at Redstreak campground in Radium. Visit the hot pools.
Drive through Kootenay Park (1 hour to Hwy 1 with no stops then 20 minutes more to Banff) to get to Banff. Then resume my previous tour by heading back west to Lake Louise.
Campgrounds in Kootenay Park other than at Redstreak are unserviced and the only one you might fit into would be Macleod meadows. The Paint pots in Kootenay park are interesting as is Marble canyon though the parking at Marble canyon can be an issue for big rigs.