Just got done with that trip! Yes, 98 is an excellent 2 lane road. Judging by the traffic, it is a major RV artery, lots of Class A's and Fifths that made ours seem tiny on the route. Watch for the turn in Kayenta onto 98 - it's not that obvious, and we blew past and had to go back.
There's a time change from Monument Valley to Wahweep. We arrived an hour earlier than we planned, but the site was open, so they let us check in.
Wahweap is a great campground, facility wise. WiFi is typical campground - barely useable. Avoid the camp store, prices are sky high. Laundry is pretty good, especially the dryers that are relatively speedy.