The inner rails appear to be 8020 quick frame material. I would be careful with using the 8020 quick frame connectors when they are going to be subjected to allot of stress. This year our team may use the quick frame material however for stressed and load bearing connections The E-Z tube connectors are much better. They do not match the Quick frame tube dimensions but, a little filing takes care of that. They are available with and without internal steel welded reinforcement.
http://www.eztube.com/connectors/connectors.html
If the Quick Frame flange tube was used you would have a support for a board to lay in the center to add stiffness and mount stuff. How are you going to attach the quik frame to the c channel?