I use Google Maps and utilize the “Add a stop” function to customize the route. However I’ve not found a way to save the custom route to Google. But, you can “share” the route (copy the link) and save it for later or share it with others.
Be aware that as you are driving the route, Google may change it on the fly to accommodate for traffic etc. It will briefly prompt you to accept the new route but will change it if you don’t reject the change. This can be a problem if you are trying to avoid parkways, propane-free tunnels etc.
I also use Allstays Camp & RV to find places to stay such as campgrounds, rest areas and Walmarts.