Generate a .gpx-file with campings as waypoints near your route.
If you have a smartphone and don't mind using it while on vacation, this tool probably is not worth your attention.
However, If you are a user of simple but sturdy GPS-devices like the Etrex 20x, you enjoy being off grid, you don't have a smartphone ... this tool might be really interesting. By putting a file with waypoints representing 'campings' on your GPS, these campings will show up as little tents on your map. When feeling tired, just zoom out a bit and ride to the nearest tent.
The data used for this application comes from the magnificent Archies campings where you can download waypoints of campings per country (In Europe). Sadly, Archies waypoint files are sometimes too big for our simple devices. With big GPX-files, they tend to boot very slowly or to not even load the complete files.
The obvious workaround is limiting the waypoints on your device to only the ones that you will need, those near your route. And that is exactly what this tool does.
After uploading your GPX-track and downloading the generated waypoints-GPX, just put both files on your device. In contrast to the GPX-track, you don't have to 'load' the waypoint file on the device. The camping waypoints will always appear. Note that you might need to tweak some display settings. (By default, most Garmin devices hide waypoints when zooming out beyond a certain scale). For Etrex devices go to Setup -> Map -> Advanced Map Setup -> Adjust Zoom Ranges -> Zoom levels -> User Waypoints. Here use a setting of at least 8km.
BAD: All the campings of France and one route.
GOOD: Only the campings near the route.