Don't laff-get a handful of the 'dollar store' turkey flavour injectors. You can inject epoxy thru holes drilled along the fin root and CR (front end) For a real adventure, (practice this first-everything happens really fast) set up two part foam loads ( I used 3 basters for this) by measuring the base in three separate cups (be mindful of the capacity of the baster) and three cups of catalyst. I used straws but you can use clear tubing (like aquarium air tubing) glued/taped to needle outlet to make three injector 'kits'. position these at the end of the rocket in each 'fin pocket' with the rocket standing 'upside down. It helps to have an extra pair of hands for this. Put the base in the injector and then add catalyst and stir with a chop stick and QUICKLY insert the plunger. Do this quickly for all three bays. The expanding foam will fill the cavity and you can trim out for your final CR install. Crush it down for your epoxy bond on the forward (inside) edge. Note you cannot have the motor retainer on the motor tube at this time. As usual, mask and keep all areas from the dreaded 'foam overload' as it expands up (but hopefully not over the end of the tube). I think I used acetone to remove the sticky overflow before it cured. Yes, this is a pain in the ass to do, but is a really strong fin can. Make sure to do your Cp/CG calcs afterwards. Be sure to use newspaper to protect any carpet or surface you are working on. Don't ask for details about THAT! Straight smoke and good chutes!