We didn't have a bit of trouble with our 27' Four Winds Class C and a pickup/huge camper in Arches, as there is easy access & parking. The main parking area at the Delicate Arch trailhead has a large vehicle area. There's plenty of paved pull-outs and several dirt areas just off the roads that are plenty big enough for class C motorhomes.
The only issue we had was the ford frontend fell apart after it was aligned at the ford garage.
Just as others have said, get an early start, go all the way to the end, and work your way back out. Take your time; you might want to spend more than 1 day there. I wish we had the time to explore way more than we did, but we thoroughly enjoyed all we saw.
2016 Forest River Sunseeker 2250SLEC Chevrolet 6.0L