Mack bought, built and.. boring?
How about making a new trailer for it? Let's say that I was bored and decided to rebuild 42078 into something different. But after disassembling the trailer, I thought that it could be rebuild into different trailer. The trailer has only one function, landing gear. Operated by levers on either side of the trailer: Being built from limited amount of parts, it has one flaw - can be driven only on flat surfaces, due to minimum spacing between its frame and truck's rear: You have been warned :P And if some would like to build it, here are free instructions: https://bricksafe.com/files/M_longer/42078-alt/flatbed/42078-Flatbed.pdf
(Mack model made by Philo) Sample pages:
After approval by Rebrickable, it will be available with parts list here:
https://rebrickable.com/mocs/MOC-12680/M_longer/42078-flatbed-trailer/