1:17 scale Lowboy trailer in black
The jeep component can be found here http://rebrickable.com/mocs/motomatt/lowboy-trailer-jeep
I used to use a custom version of Ingmar's lowboy trailer
https://rebrickable.com/mocs/2legoornot2lego/trailer-tr4-mkii-with-instructions to haul my 42030 Volvo Wheel loader, so I utilized the same gooseneck attachment geometry to allow both to be interchangeable. The gooseneck is based on Ingmar's design but is meant to be operated by a hand crank and manually locked in place using an 8L axle with stop.
The instructions and parts list here are for a black version with white and orange side markings which fits well on the back of my http://rebrickable.com/mocs/motomatt/peterbilt-389-daycab-semi-truck-117-scale-in-black-and-orang. I think it could also be easily built in other colors, such as yellow to go along with construction equipment being hauled.
Waiting for Inventory to load
These types of files are created with the LDraw system of software. You will need to install compatible software to open and view the instructions. A full list of available software is on the LDraw site.
This MOC also has a 3D digital file available (eg LDD, MPD, etc): 3D Model