I don't know about a trailer, but a plain flatbed version of the HEMTT would be great for use with attachTo. Like this:

http://en.wikipedia.org/wiki/File:Hemtt_iraq.jpg

My community has been experiencing this issue as well. Looking at NBRC_FOX's crash files, I seem to be getting a similar crash log. I attached my dump as Raws_ArmA_3_Crash_Files_Issue_0013407.7z.

We noticed the following on a co-op mission with five player slots:

• Filling only one player slot does not cause a crash, and the one player is able to enter the game world.

• After one player successfully enters the game world, other players are able to JIP successfully.

• Filling more than one player slot consistently causes all players to crash to the desktop after the briefing screen and before entering the game world.

• Enabling and disabling AI for all or some of the unoccupied player slots does not seem to affect whether players crash; e.g., if two players join and the remaining three slots are filled by AI, the two players still crash to the desktop.

I'll try to get a few more people who have been crashing along with me to submit crash dumps as well.