Hi, Jim and Sue. On last year's "big trip" we stopped at 4 of the 5 national parks in Utah. All were fascinating and the geology and geography were so different from what we see every day in the PNW. Arches NP was so HOT we didn't want to leave the car. That said, the Utah NPs and the Grand Canyon are awe-inspiring. Interestingly, they are all part of the Colorado Plateau but at different elevations. We stayed at KOAs in Panguich, UT (cute little town), Moab, UT (great bathrooms w/showers), and Alamosa, CO (to be honest, can't remember it!)
In April, we stopped at the Homestead National Monument of America in southeastern Nebraska and the George Washington Carver National Monument in southwestern Missouri. Since you're both history buffs, I think you'd enjoy visiting them. We did spend one night in Eureka Springs, Arkansas. We didn't spend any time exploring except for when we got lost, but the town looks like there're lots of interesting sights/shops/restaurants. It's in the Ozarks and I understand it's quite the tourist destination, similar to Branson, Missouri.