Logging on a trail map

So I made this:
...and I wanted to try it on a trail map, but there's no log kiosk, so I made another addon for logs ontop of roof which is exactly the same but has no loadpoints so I can attach it in the garage. And now I want to do the same to the trailer logs but I don't know how to make an addon for a trailer or if it is even possible. Any help?

Ok, I've got it working, I just need to "drive" the trailer using the spawn option in the dev tool so I can attach an addon.