interesting idea: plant box and belts . Hook together several belts to be large enough to go around if using real leather belts (from thrift store) . these "belts" look more like strap webbing and could be DIY made to size.
*3 metre PLANTER WITH TRELLIS* IN BLACK | Trade Me
How to Build a Simple Entry Arbor This arbor is easy on the pocketbook and a snap to build. In fact, if you like, you can eliminate most of the cutting by asking the lumberyard to cut the wood to length for a small fee.