Locally there are two old box cars that are not anywhere near apparent railroad tracks. Both fo course are to close to where tracks used to be. Neither are on Trucks or wheels anymore and will likely never move as the worth in Semi-dry storage is higher than the scrap value of the steel. One is at a local hardware/surplus store in a building that at one point had a siding MANY years ago. The other is at what was once a local oil distributor again it is not far from track adn there may have beena sidign ther at one point?
The non-rolling billboard is a neat concept.
The only other non-rolling stock locally I can think of is the old Tank car on concrete pylons that is now gone at the Arcade and Atticca RR. IT was a fueling station at one point I believe?
Stampin' Up! in Kanab, Utah has several box cars. Nearest railway I know of it the UP in Cedar City, 60 miles line of sight, about 100 by road. Not sure what the deal is, because as far as I know, Kanab has never had any sort of rail service, even 1800s NG short line stuff.