HELP--planning 7000 mile trip.....

I have free Allstays app on my phone. You can ckeck it out on the web first if you want. Also look at Ultimate Campgrounds app, for $3.99, very thorough and detailed.

On our recent trip, I selected the route (Indianapolis, IN to Custar, SD). Then determined how may days we wanted to spend traveling. We selected 4 days travel to get there.

I then took the total number of miles and divided by 4. I then pin pointed on a map where those 4 points were.

Then simply did a Google Search on Campgrounds for the nearest city at each point. It turned out we did about 350 miles each leg of the journey.

Our return home? We planned on 4 days, but decided to select the route after we reached our destination. The day before we left, I went through the same exercise as we wanted to travel a different route coming home. Turned out, the first leg was closer to 400 miles, but right there was a KOA campground. We spent the night. And the next leg of the trip ... well ... we drove straight home and got home 2 days early. That turned out to be a good thing, although it did mean a very long day driving.

Also had luck asking locals, or some bigger small towns have visitor centers/chamber of commerce. Sometimes local fairgrounds are available.

I have an early model Rand McNally GPS. It has many campgrounds in the software. You can look up COE, National Forest and other government campgrounds. You can ask close to you or close to a city.Phones apps do not always work as they rely on cell service which may or may not be present.
US campgrounds does work for me while planning at the house.

There are several smart phone apps that I've been pretty impressed with. The one I use is RV Parky, tells you all the camping and parking areas near a location that you input. Most are free, or little cost.

X2 on US campgrounds...topo/elevation feature lets you find CGs at elevation for cooler boondocking.

Can't recommend .......this GPS/backup but it looks interesting for the price. Scroll down and you will find several more.

Although not all inclusive, this site may help with some of your campground planing.