This is a lowboy trailer with a detachable gooseneck which I built to transport my 8043 excavator. The original version did not utilize suspension and was purely a shelf display model. The parts list here is for version 2 shortened by six studs, which uses shock absorbers and PF lights.
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.