Lots of ways to paper fins, but I use 65lb. cardstock (feels like heavy typing/printer paper). I brush fins with Mod Podge, then apply paper and press this sandwich between glass plate for 24 hours to prevent any warping. Use a few heavy books for weight on the glass to keep them flat and wrinkle-free.
If I want tapers on leading edge, I sand balsa tapers, and use a one-piece fin cover folded at the leading edge.
My covers are cut slightly oversized and I trim once they are removed from glass press.
I seal paper edges with thin CA to prevent lifting.
Then glue to body tube, fillet as usual, and prime and paint as usual.

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Lee Reep
NAR 55948

Projects: Semroc Saturn 1B, Ken Foss Designs Mini Satellite Interceptor
In the Paint Shop: Nothing! Too cold!
Launch-Ready: Farside-X, Maxi Honest John, Super Scamp