I'm a meticulous planner and I almost never make reservations until the day of. I hate to schedule days and times. But what I do do is preplan.
Before the trip I lay out waypoints about every hundred miles, then I find three potential sites near each waypoint. I try for one free (Walmart, rest stop, BLM, etc.) one park (national, state, or BLM) and one private (RV park). We keep a printed trip sheet with the waypoints and the names and phone numbers (if available) of the sites. Dailey drives are 1, 2, 3, and occasionally 4 waypoints, depending on what's happening at the time. If we intend to stay at a park or RV Park, we call after lunch for a reservation. There have been times I've been hoping for a nice long hot shower and we ended up in a Walmart lot, but I've never not had a place to stop.
I've started calling the Walmarts as part of the pre-planning, just to confirm they allow RVs. More and more don't.
I use freecampsites.net, recreation.gov, and Allstays.com. I also find state park websites.
Imagine XLS 17MKE and Transcend Xplore 200MK are good choices for freestyle traveling. Shorter is easier and you want to be able to use the trailer with out extending the slide. Its considered bad etiquette at Walmarts and rest stops.
Last bit. It is harder to get spots in State/National parks on weekends. We try to be on the road (free) Friday and Saturday nights and in parks Sunday through Friday morning. Less people in the parks too.
Can't get the Murphy bed down in a 17MKE with the slide it.