OK,
some pictures, I think, this is my entire collection of prime trailers. I think.

This is the Fansproject trailer,




The hitch doesn't fit, it is designed for the voyager from several years ago.


This is the Ultimate movie prime trailer it kind of fits, I don't think the peg sat in the hitch properly though.



It does open up, but there is no room inside for anything ;-)


G1 reissue trailer, clearly the wrong scale and does not hitch.





This is the Mechtech trailer that was available a couple years ago for a deluxe prime I think. I picked this up off the eBays as a bootleg, it works OK with the voyager movie Galvatron. doesn't work with this voyager prime particularly well. it will sort of hitch but it separates the legs, making it then fall out of the hitch.





the inside in case you're curious.