Mark, thanks for the explanation, and Andy the photos tell a lot about the design.
It appears that the tube frame does not extend to the rear completely and the front mounts and a tube extended part way back to the middle of the tank take the load. You are correct about the straps! If loose they allow the tank to pivot on the front mounts more freely. Box tubing would have less flex than round tube for that center tank support.
It makes one wonder why frame was not taken to the rear to hang thing like the tanks
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