A custom trailer by "Best Toys," that works with all Classics and Henkei Optimus Prime Figures. Opens up to reveal repair bay inside, and can store 1-2 Classics figures inside once closed. There is also a detachable wheel section that is roller as seen in the images. Originally available as both a Silver and Red Version as well as a Black Nemesis Version, and currently Purple Shattered Glass and Clear...Ghost? Cloaked? versions.
In addition to this, a later clippy dealy was released which allowed the trailer to work with deluxe Animated Optimus Prime as well. Kinda neat.