I add to Richard's comment regarding techniques used in aircraft - the book: Construction of Tubular Steel Fuselages for example has a great amount of info that could be helpful for an LSR project. It may be a good basis to start a dialog with tech inspectors.
You can now even download the book from
http://www.actechbooks.com/subcategories/38/One reason to leave the corner open is to avoid too much welding in one area leading to a weaker weld and/or stress fractures; and only one side of the gusset is welded, either both on the same side or alternating.
Now some of you may ask why all this airplane stuff? Well, in LSR - isn't the goal to fly really fast without lifting off?
Michael Werner