Haul-U Transport is an obvious ripoff of U-Haul. It appears as a large grey container trailer that is towed by the Peterbilt 379 in this game.
The trailer spawns near the tractor when you start off the game. Back up the semi until you hear a loud banging noise. That is the noise of the landing gear going into the trailer, which is quite strange, because landing gear isn't supposed to go all the way into that thing. You cannot open the back doors of this thing but they only open in the mission where Badhand forces Tanner to load cars into the trailer.
There is a glitch where you can pull the container chassis. This only occurs in Nice. Come close to the trailer until you reach the middle or the end of the rails on the side of the trailer. Press the enter vehicle button and you'll see Tanner walking like he is trying to get in the trailer. Break his attempt to try and get in the trailer and get back in the truck. Drive off until the trailer disappears and go back to the trailer. Now the trailer is a container chassis, but it looks more like a flatbed trailer and that fucking confuses me.
The trailer has its own breaks. Just press the break button on when driving your truck and you'll see the wheels of the trailer stop. The thing doesn't have working tail lights and turn signals. Awkward because it needs the tractor to power the breaks but the tractor can't make the lights work. Fuck, the tractor doesn't even have the airhoses for the trailer yet it can power the breaks.