Regarding the trailer-
I have looked at 2 photos of the trailer taken by the neighbour in one of them you can see a lock on the door, and in the 2nd one, to me it looks like a lock cutter on the driveway.
So this would mean the trailer was not accessible to someone who did not have keys. I know someone who has a similar trailer, and on the back door there is what I believe is called a cam lock. This is much like a car door lock, and requires a key as well. I personally have not seen a photo of the back door of the truck to be able to tell if this is the type of lock it has, but IMO it would have a lock of one kind or another to keep it's contents safeguarded. What I am getting at here is that whoever loaded the truck into the trailer must have had whatever keys were required to open the trailer, and if it were not DM as so many are suggesting, how did these mysterious people get his keys??? And how did he not notice his missing keys???
And another point, where did DM keep his trailer, and if it were suddenly missing, would he not notice, certainly more noticeable than missing keys?
https://twitter.com/mcianf/status/334326749921951744/photo/1
https://twitter.com/mcianf/status/334326998631591936/photo/1