JST posted this link earlier - shows where the Superchargers are, including those under construction. Tesla is enabling many routes for long distance travel.
Http://supercharge.info
The car also knows where Superchargers are and routes you to them, and it shows how many stalls are in use. I have had to wait to charge once, but years ago when there were fewer Superchargers, and it was right after the owners conference ended, so many of us needed a charge. Only waited for 2min...
For other charging options off the Supercharger highway, RV parks come in handy. I used one in Page before the Supercharger was built, and another near Monument Valley when we visited for a couple nights. Tesla is planning a Supercharger in Kayenta that would work in future... There are also many hotels that have added chargers for overnight charging — on our 4500 mile trip a couple years ago, 8 of the 9 hotels we stayed at had charging...