Inside this is about a 2” square one leg could slide down into.
Using a round leg for this side would allow you to pivot the stand around the tube, while 2” square pieces everywhere else would be strong enough to not need any guylines I think

https://i.poastcdn.org/57687f2862c30cd5d89c486cdc86f8362adeccc89e11a1bbeefe715d0d5e286b.jpeg