Yes I am filling and sanding the fins off the rocket. I do this even when using Balsa Sealer, never had an issue with fins falling off. I have used sealer when the fins are attached and on a 3 or 4 Fin rocket it is no real big deal. On a more complicated build I find it hard to impossible to sand all the balsa that has been sealed 4 times. Well my experiment with FNF did not go so well. I had the practice fins already for primer and they looked good to me, so I shot the primer. When the primer was dried there was still grain showing and looks like the balsa or FNF sucked up some of the primer. I really think for FNF to work one would have to use the technique that Chris uses, apply FNF, sand and prime the parts off the rocket. I also noticed that Chris sands off most of the primer for a smooth balsa surface. For my building I like to apply 1 coat of primer followed by lightly sanding leaving the primer smooth but not sanding to the balsa or cardboard parts, then I begin shooting my top coats. I am off today and will start brushing all the parts with Brodak Sealer. Since the fins are large, I am using one of my large Camel Haired brushes I use for large RC planes that I dope. I am not bashing FNF, I have seen some wonderful rockets that were built using it as a filler, it is just not within my building and finishing right now. Also Chris has posted old rockets that he built back in the day using balsa sealer, and those rockets look great as well. I think Chris could use milk on his fins and they would still come out looking great.