Oh...you are so right T-Fanz...I never knew that or how those connections were made for that amazing big unit. T had always assumed that the trains that came with it were the only ones that could be used but thanks to you pointing it out I know I was wrong. Thank you, I really enjoy learning new things about these trains.
Discovered this video which shows the big unit and how it connects to the trains at about the 9:48 minute mark.
Also Kmott...in this same video, at about the 3:47 minute mark, you can see details of your Cargo Liner including how to stand up the PlaKids in the open bay area and how other accessories can be mounted using those holes you asked about.
All in all the video is pretty cool and, if you really get into the Hyper Guardian Tomica line you may also like the big unit in the second video.
Discovered this video which shows the big unit and how it connects to the trains at about the 9:48 minute mark.
Also Kmott...in this same video, at about the 3:47 minute mark, you can see details of your Cargo Liner including how to stand up the PlaKids in the open bay area and how other accessories can be mounted using those holes you asked about.
All in all the video is pretty cool and, if you really get into the Hyper Guardian Tomica line you may also like the big unit in the second video.