George's Workshop Solar. RIBS - External ribs form the parabolic shape to the reflector sheet.
There are seven ribs required for a single eight foot reflector or three ribs for a four foot reflector. I recommend MDO wood (weatherproof sign board) and suggest sources of supply (start with your local signmaking shop). DIY Tracking Parabolic Solar Concentrating Trough. Parabolic Solar Collector Ver. 1.