Is there an entrance/exit at the west end of the park, with access to the main entrance?

Yes, South Boundary Road is East/West road through the park

Some of the best waterfalls are on the west end at Presque Isle and theres a parking lot and campground and a ranger station where you can buy a motor vehicle pass all on that end.. And then as stated by others you can drive south boundary road around the perimeter of the park to get to all the southern trailheads and the visitors center and union bay campground. Check out summit peak and the nonesuch mine ruins!

There's plenty of room for a large RV

There is a back road that will take you into the park at the West end.make sure you pick up a park map.To find all points of interest