Start off by loading up the map 'Island' on Casual using the map default vehicles. What you want to then do is attach the 'Log Carriage' to the 'C-255' vehicle and drive out of the starting location and take a hard left where you will immediately see a small raised rock to the right side of the path. Position the rear end your 'C-255' in line with the rock so that it looks something similar to the image below.
Once you have your vehicle in place you can switch to the 'A-469'. What you are going to need to do is use the small raised rock as a kinda ramp in order to get on to the carriage of the truck like the image below.
Once you have the Jeep on the trunk, I would advise applying your park brake so that it doesn't roll off the back. Switch over to the 'C-255' truck again and slowly drive off to the right along the shoreline (Be careful not to go too fast as there are many rocks around which may damage your vehicle). Achievement should pop around the time you reach the river nearby.