I think they shoot in the same hotel room, so either they have an agreement with a small hotel or it's a love hotel.A lot of scenes seem to be shot in real hotel rooms (not filming sets) though. I wonder if they just book a regular room and then a group of crew go up with with cameras and lights in luggage, then the JAV actor and girl to up and they are shooting all day (usually looks like daytime when they start and then end at night by the light in the windows).
And when it's not packed or the room are well soundproofed to hide the over the top fake girl reactions in some JAV. Because if I'm a customer next to the room, I would be the first to urge them to shup up before I kick their asses.JAV studios know which hotels are 'safe' to film at (ie, elevator can't see lobby so they can secretly send up staff members).