Raised garden planter boxes on wheels / casters - Size is 2 x 4 each, just over 4 tall with the casters installed on the bottom. Soil depth container is 12 and the bottom shelf has about 3 of clearance to hold drain water trays.
this would work to support the blackberries without having to stake and tie them all the time -- Upcycle old wood pallets into awesome raised gardens. Wood pallets are so cheap and make building a raised garden bed super easy. It only takes 9 steps!
How to reuse pieces of an old garden hose (Alternative Gardening)