Here's a starter:
How big are the largest transport trucks in Japan? In America, what are known as semi-trailer trucks or 16-wheelers are massive enough inside you could easily stage porn scenes. Filming inside an actual truck trailer would likely be too hot, to restrictive, but as a set, you could assemble your simple, but believable background walls from wrecked truck trailers. Then you only add context scenes, possibly on location, using real truck trailers.
The gimmick that would add the variety to a series of vignettes or even a series of videos would be "the props"--the stuff the trucks are hauling. Without much thought I could imagine grocery produce (crates or boxes including cucumbers, squash, etc.), hardware supplies (including rope, for a bdsm-themed encounter), furniture (bent over desks, surrounded by chests with mirrors), and the inevitable cliche--a truck carrying adult videostore supplies. The selling point to a producer would be that any imaginable fetish object or sex prop could logically be found in a transport trailer.
There are several possible plots that get the girl in the trailer where she would have sexual encounters with the drivers or warehouse workers: a stowaway just trying to get to a new location for free; a victim escaping (maybe naked) from a gang or an abusive husband; the trucking company secretary checking inventory who gets trapped in the truck by accident; or just a girl on a dare by friends or her perverted boyfriend.
Where the truck is when the sex takes place also offers options that change the storyline. At the warehouse being loaded puts lots of male laborers in proximity. At the delivery point does the same. On the road at a rest stop or stopped for repairs in a desolate area gets the driver into the trailer, or at a truck stop more drivers could get in on the action. Maybe the driver pimps the girl, collecting money from the other drivers in the parking lot.
It might be too expensive to engineer the set, but showing sex on a moving truck (and I mean filmed on a set made to look like and be rocked like a moving truck), swaying down the highway or across bumps... that would make for some interesting choreography for dicks in orfices!
Well, that's my sample idea for a new location to stage a variety of scenes. But obviously my conceptions are driven by images of the trucking industry in America. The size of the trucks and typical driving locations and circumstances in Japan could be totally incompatible.
Maybe this idea has already been used, but I'm just unaware of it. Please feel free to critique or elaborate on my simple idea. Post fantasy scenes that would fit this one. Or even better, post your own conceptual ideas. There are plenty of people here who can make this an entertaining as well as informative thread. So run with it. Make a producer rub his chin and say, "Hmmm." Or make your fellow reader rub his cock (or her vagina) and say, "Ahhhh!"