In DOTM, while in Chernobly, Optimus was with his trailer, which turned into a weapon platform upon Shockwave's show-up. When the autobots rolled to the space station to take off in Xentium, Optimus was with the trailer at first. But when he and sam were saying good-bye, the trailer dissappeared. The autobots turned up again in the later part of the movie, after their "feign-death" by dropping into the Atlantic. Then Optimus said "bring the war to them". The trailer was not seen there. When autobots planned to break into the beseiged city, Optimus transformed into truck and the trailer was with him once more. But the trailer was toppled by the driller and seemed not be of use any more. Where did Optimus "hide" the trailer after Xentium and before final battle.