Personally, I would use 2024 aluminum tube rather than 6061. It's about 50% stronger.
2024-T6 yield is closer to 50kpsi tensile, while 6061-T6 is closer 40kpsi tensile. The biggest issue with 2024, is that it's extremely difficult to weld if it becomes necessary. And welding many aluminum alloys (the ones that are weldable) will significantly reduce temper, forcing post heat treatment to restore it.