I know of a motel/RV park south of Vinita, Oklahoma; another just west of Louisiana, Missouri. Have seen a lot on eastern Kansas, Illinois, Missouri, western Indiana: corn country. Motels are used by harvesting crews in season. Most of the locations I've seen are pretty bleak for family gatherings, accommodations are for people working hard 16 hours a day, just sleeping on off hours, so not much in recreational facilities.
Suggest looking for (rather than motels) :
Family campgrounds with both cabins and RV sites, such as KOA and Jellystone, and others non-franchised.
RV parks or resorts with rental trailers (some membership resorts are in this in a big way, kind of a condo trailer thing).
State parks with cabins. I see these everywhere, CCC built a lot of cabins when they were building parks in 1930s. Some states have kept it up. Cabins may not be in same place as RV campgrounds, which tend to be 50-80 years newer than either cabins or tenting areas, but there will be common places everybody can get together, picnic shelters or meeting rooms. Our family has been doing reunions in state parks since late 1940s, Ohio and Pennsylvania, but many other states have similar facilities.
In-laws, oldest daughter's family, finds park facilities like this in Arkansas, Texas, and Louisiana. I suspect more states have them, if you check websites for park systems in Ohio, W Virginia, Kentucky, Tennessee.