All of the classrooms are sets. Just look at the windows, they're always just squares of white light or non-existent. As for buses and trains, they seem to own them. It wouldn't be too expensive to buy a retired one. I always get annoyed as all the bus chikan JAV are filmed on the exact same bus. Train carriages and elevators too, you'll notice there are some shots that are logistically impossible unless there was a wall missing.
I'm more curious regarding outdoor JAV, it seems that they just go waaaayyy out into the countryside but when it's a convenience store? It's highly unlikely that they'll go into the trouble of buying all those goods and building a fake one.
There was also this one AV that was set as CHIKAN IN LA! and the public bus stop as well as the bus was obviously American (not a yellow school bus BTW) as well as everybody except for 2 Japanese danyuu. Did they seriously fly the two of them out to ‘Murrica or just find some sort of similar location in Japan?