I haven't used them, but from what I've seen they should be plenty strong enough. They appear to be Dubro's answer to Nyrod and as such should have similar qualities.

The most important thing you can do is brace them about every 3" or so. You don't need a full former. Just cut some 3/4" wide rectangles from 1/8" balsa and drill holes in them for the outer tube. Cut them to width and glue them inside the fuselage. You should probably reinforce the joint on one side with 1/8" square balsa so they don't pop loose.