Bob, I did some mods replacing the main spruce spars with basswood, this will save some weight. The wing tube is about 1 inch and is strong enough to replace the big and heavy plywood that joins the wings panels. I cut pieces of basswood and filled the space between the wing tube and the main spars, then I glue four pieces of share webs on each side, it goes from the top of the main spars to the to of the wing tube, same thing on the bottom. Then I filled any gap between the wing tube and the share webs with epoxy. It is very strong.