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Steel has 3× the tensile strength as aluminum, so the aluminum would have to be 3x thicker to accomplish the same task, also the 100's of rivets used for assembly would be 3x as likely to fail because aluminum is too soft
Aluminum wouldn't hold up to the tonnage of most people anymore...
I know it would add cost to the unit , but my GOD the weight savings would be worth it ! Those steel frames are super heavy , then they use aluminum tube for the tent supports ? Extruded aluminum seat frames would be sweet ! Eskimo and the rest are you listening ?