I'm doing almost the same thing right now to a Tiger 60. I'm useing a 3/4" alumunum wing tube designed for a AT-6 with a 91" wing, it's 28" long. My wing is 74" and I will have 12" in each wing supported with lite burch ply 1/8" thick fore and aft of tube reciever. If your intrested I can tell you how to make a fiberglas tube right on the aluminum tube, it's trickey but can be done, I just did it.

I'm building my plane at Goldberg Tiger Club in this section, check the last page, just posted on the 26th.