Since Glacier NP would be a big highlight of your trip, I thought I'd make sure you know that Going-to-the-Sun Road (the whole middle traverse of the park) has severe vehicle size restrictions. The info is surprisingly hard to find on the park's site so here it is:
... To help reduce congestion, vehicle size restrictions are in effect. Vehicles, and vehicle combinations, longer than 21 feet (including bumpers) or wider than 8 feet (including mirrors), are prohibited between Avalanche Campground and the Rising Sun picnic area parking. Vehicle and vehicle combinations over 10 feet in height may have difficulty driving west from Logan Pass to the Loop, due to rock overhangs. Stock trucks and trailers are able to access Packers Roost on the west, and Siyeh Bend on the east.
This ALSO may impact having the dog along, since if you need to take a shuttle or one of the tour buses, I"m sure that would mean leaving the dog at your sister's RV.
Almost all parking areas within the park are crowded during the summer. I"m hoping someone has a toad for touring inside the park. I know it sounds like lots of hassles (and it can be), but it really is a spectacular place.