Not because I'm in the screw pile business.... but if it were me, I'd get some screw piles installed I 2 rows, about 8 to 10 feet apart along the trailers I beams. Have the piles above the ground just high enough to back over them, about 8 inches is typical. We make an adjustable bracket that slides into the pile so after you've driven over the piles slide the bracketsame up pin in place and fine tune level with the threaded rod cap..
Some 10 mil poly on the ground, some clean sand on top of that and decent t skirting..and viola...a not so permanent (can unscrew the piles when you want to move) permanent foundation.
Feel free to contact me if you want more details. I do one of these every week.
2017 Cougar
2015 Ram 3500 Megacab 6.7 Cummins Aisin transmission