Hi we are visiting from Australia & plan to visit Yellowstone NP in late May in a 31 ft R ( we pick up the RV near Chicago May 17th & drop off in Denver on June 2nd). I have read that the roads in Yellowstone may not all be cleared until Memorial Day. Is it likely that we could approach from Cody & see most of the main sites by then or will it be difficult to drive with such a large vehicle? Also would we need to book an RV site at that time? We may only have 2 full days & 3 nights there, so advice on what's best to see with the time constraint. Also how long would it take to get to Denver from Yellowstone if we wanted a quick look at Grand Teton on the way. We are considering a detour up east Michigan to UP Michigan on the way from Chicago & wonder if this is worth it as we will miss seeing Rocky Mt NP in Colorado. Unsure of what is best to see???