Central Florida to Grand Canyon

Agree with Jim@HiTek and Janss about crowds, temps, and places to visit when you get there. Summer is tourist season and it's busy, spring or fall would be better, but you don't have that option. If you just want to see the Grand Canyon SR itself, you could leave the rig at the campground in Williams AZ along I-40, and take the GC train up to the canyon and back. As a day trip. The GC rim trail is a few miles long and goes through all the popular lookouts along the way, and if you get tired you can take a shuttle back to the GC Village. North Rim GC and Bryce Canyon NP would be near top of my list. Lake Powell near Page AZ good for recreation. Durango and the 4 Corners would give you multiple options for places of interest, too. If you have the time, why not do a coastal trip along the Gulf through Mobile AL, New Orleans/Baton Rouge LA, and maybe plan stops or short side trips along the route through Texas? Lots of options along your route for interesting and historical places, assuming you'll use I-10 west. Make it a long loop tour, with stops along the way.