For sure you can't take a 36 foot 5th wheel on Going to the Sun Road. They won't allow it, and it would be suicidal to try it. Frankly, the best way to make that trip is via the FREE shuttle bus that will allow you to hop on and hop off at stops all along the way. It is a great experience, and beats hell out of driving and fighting the traffic. Going To the Sun Road is a narrow, 2 lane track that is often bumper-to-bumper in both directions. It is a twisty track you cannot travel quickly because of the traffic. But the views are second to none. Take your camera, and remember to dress warmly, because it is singularly beautiful at the top, but always cold. There is a reason they call it Glacier National Park.