I found some acceptable plastic for the fins. The material isn't crystal clear but is good enough for this rocket. I first roughed out the pattern in cardstock and found, because the base of the paper version has been rebuilt a few times, each fin required some tweaking. I designed the fins to they would abut the small paper fins and follow the contour of the nozzles. This added more area and provided better attachment too. I attached them with hot glue. Note there is no detail photo of the fins. Like I said, they are good enough. The CG moved back about an inch, but it should be quite stable with a C11 installed.
This will be my last post on this build until it flies. I still need to add the launch lug and have decided to plug the tube in the nose section with a foam board bulkhead. I wouldn't want the nosecone to blow off on ejection nor would it be good for the 'chute to get blown up into that tube.