Don't forget that Tesla will probably end up building the most number of chargers over time. Charging is its own business with its own margins (e.g. Supercharger network). In other words, it's a source of net income for Tesla so as they build more trucks, they'll build more chargers as they've done to date with passenger cars and Superchargers.
What if it's not and solely powered by solar (just wondering - Megachargers most likely need help from the grid).
Maybe a huge charging station which has to have large buffer batteries anyway would benefit from a large solar-panel field nearby / above it, if land price is acceptable. That would be a natural extension of the solar roof business.
Chargers at truck stops can only be good for their margins, who would have to cater to people waiting for their trucks to charge on things they actually make money in (hint: it’s not diesel or electrons).
You might see truck stops adding "public" chargers after that EV trucks become commonplace (in the same way that truck stops have fuel discount programs for member fleets) but how will EV trucks going to become commonplace if private operators using their own infrastructure are 99.99% of users?
Truck stops are thin margin. I don't see them making the investment without a need. Maybe if a big player (e.g. Swift, Walmart, etc) wants to convert to EV and kicks in a bunch of money to have their fuel partner make the capital investment. But I don't think that's going to happen until EVs are so good that it's a "profitably without nearly any doubt" type investment. You'll probably need to see a decade or two of short haul EV trucks and the accompanying refinement before that happens.