I have 2 trailers like your first picture.
I like the taller box with the double cylinders.
The tail gate looks light duty to me (just saying)
The problem is the 12000lb trailers are to heavy to pull every day, It costs me 40 bucks to drive around the block .
I bought a 6x10 dump to pull for smaller jobs plus the 12' trailers is much harder back into drive ways .
The equipment ramps are way to heavy to load at the end of the day , i use a set that i bought on EBay for 400 bucks and slip them under the machines after i chain them .
I could load a 8000lb Min EX into a 12' box but the boom would ride chained on to the trailer tong .
I would get some funny looks from the DOT boys . but i was not stopped for that .
To balance my trailer with my skid steer i needed to back in and hook the bucket over the tail gate or i would have to much tong weight.
It hard to chain equipment inside the closed box .
The worst news is if you get a low profile trailer you cant dump mulch into a wheel barrow you will have to hump it off the ground . I love multitasking but You will need a trailer for your mowers . If you must mulch out of a low trailer you can hang a sheet of 3/4 ply wood over the tail gate and into the bed to dump up high . I'm liking a 14' 14000lb trailer with drop down sides for your needs . John