1. Square tubes ,37% stronger than round pipe 2. ISO9001 3.Covering 10 countries,20years durability 4. easy installation HIGH TUNNEL GREENHOUSE The HIGH TUNNEL GREENHOUSE stand alone Cold Frame combines state of the art technology with a proven common sense approach to construction.1.INSTRUCTUREa.Included in the HIGH TUNNEL GREENHOUSE is a long list of outstanding features includes: . Square tube ...