As some of you may know, you used to be able to attach the trailers in this addon to the trucks using another addon to enable the connections, however that addon has since been removed.
However, there is now a new addon that will work as a replacement (and sortof works with old ones, though seems to be some issues there) called [Simfphys]Trailers Reborn which would be nice to see replace the old code. There is documentation about that right here[github.com], incase the original creator or anyone else wishes to replace it.