RE: Please Help
Are you welding these parts together or drilling and bolting ?Whatever ya do BE SAFE.
You could fasten those 4" square steel female threaded pieces to the bottom of the stand. These are those pieces where you could screw in galvanized pipes which act as table legs.I've seen them on the bottoms of some home made tables. Then screw in about 8 inches of galvanized steel pipe. Your tubing ladder could slide up into the steel pipe. YOu could also drill through both sections and add a cotter pin for safety.
PS You are also going to have to have a brace running from the back of your platform down your latter about 30 " I also would have made the top of my ladder as wide as your platform. Looks kind of scary. And...I always make the bottom of my latter wider at the bottom for stability.
Good luck