Warning....,
Do not use K&S streamline ali tubing for wingstruts on a 1/3 scale Cub - they are just not strong enough!! You need quite a bit more wall thickness to make it a proposition.
They migh just make it under tension, but any negative G's will surely make them somewhat unhappy......
However, you can safely use them if you run something through them and use that to fasten at each end - like a 4.40 rod - just run it through and plug the ends of the ali tube with whatever will allow you to finish it to the right shape and keep the rod centered in the tube. Then you get to use standard RC fittings as well.
Alternatives could be from Sea Commander (makers of fantastic scale floats & Canadian too!) - and are suppliers of heavier wall streamline tubing -
http://www.seacommander.com/newproduct1.asp
Or stainless steel streamline tube from Toni-Clark in Germany -
http://www.toni-clark.com/index_en.htm
My 2c.
Cheers, Mike