Most of the purpose built frames are wire, and pretty flimsy. Excuse the poor drawing, but what I'd do is illustrated below ...
Buy some suitable timber, say approx 35mm x 35mm. Cut and screw together a simple frame to surround the trough. Drill holes at suitable intervals at a slight angle, and put bamboo canes in to form the legs of a frame. Tie cross pieces on with twine or cable ties. You might also strengthen it fore-and-aft with further canes (not shown).
That should produce a simple and cheap solution that can be dismantled back to a small volume, and reused in future seasons.