How about a utility trailer?
Cover the bottom with plastic-the wood will decay in a couple of years. Fear not, they can be replaced with ease.
Mobile
various sizes
can erect sides to hold in the soil for a full bed
can use it to house containers
raised up for easy access/less bending
can build a cage around the entire rig to keep out the curious
2" tow ball is standard
put a plate on it, take it anywhere
When you get your land, the trailer will surely come in handy.
If the weight of the soil and crops is excessive, raise the thing onto blocks, or select a trailer with dual axles.
I have a 5x8 trailer, 1500 pound axle, will haul anything I need-fridge/2 round hay bales/loads of bricks/a cubic yard of compost/logs/branches/bagged leaves/mulch/lumber/plywood/pallettes