I understand you pain, anything under 55 is freezing to these bones. Williams Arizona is a great base and I really like Circle of Pines KOA. Indoor heated pool, very large sites, lots of big trees. We were there when they had an unexpected snow flurry (less than 6 inches) and they opened their Kamping Kabins to all the tenters on the grounds. Really nice people. We were in the MH, but all the same, really nice. Bearazona wild animal drive through park is a must see visit. Really. One fee gets you in, and you can drive through again if you want, we went twice. Really had and enjoyable day. The train to the Grand Canyon is a whole day train ride for a drive that only takes one hour. But if the weather is cold, it makes for a fun day. On a nice day I'd rather drive. In Sedonna the Pink Jeep ride or the Hummer Rides up into the hills makes for a fun afternoon of scenic views and Arizona history. We took the Eagles something-or-other train just south of Sedonna, that was also a fun, and interesting scenic tour of the back country. If you have time go North from Flagstaff to Monument Valley (Gouldings RV park). If you are from my generation and remember all the western movies you can look in any direction and remember the westerns of the past. Really indescribable, moving, natural wonders country. Utah has so many places to see, but if the weather is less than perfect you can head to Salt Lake City, I truly enjoyed my two stays at Salt Lake City KOA, be sure to visit Antelope Island on the Salt Lake...hard to find, only one road in across the lake, but fantastic, go all the way to the end to the old western ranch, well worth the trip. An of course there is the history of Salt Lake City and the Mormon Church. Temple Square is an amazing visit. I'm not Mormon, still a lovely visit.
Happy Trails