I have been in the business so long that when I started there were no line trimmers and therefore no trimmer racks.
My first attempt at a trimmer rack held the unit it self very tight. So tight in fact that the shaft broke just below the engine. Too much vibration coupled with poor design. Brand new Echo trashed in less than a week. I learned then to leave the design work to professionals.
I have not bought a trimmer rack since, instead choosing to keep my line trimmers on wooden shelves in my enclosed trailer. I would like some racks as the shelves are big and bulky and every time I get a new trailer I have to build shelves.
At a glance these appear to mount to the floor and ceiling which is also a great feature.