Charlie, while it's always a good thing to save weight where practical, on Pawnee-sized aeroplanes there's not as much weight savings on the fabric as one might think. A bigger variable is the weight of coating systems with the chosen system. What system does your shop like to work with? If you're doing fuselage, consider adding removable metal belly panels, which were a factory option at some point--C and D models, I believe. Adds some weight, but greatly facilitates inspection and maintenance.
One other point on glider tugs, the propwash area really takes a beating, so closer rib-stitching like the acro folks do is money well spent. Hope this works out well for you.
Thanks. cubscout