RE: v-tail fillet
Z-poxy finishing resin (not glue) with micro balloons to thicken it and a little bit of Cab-o-sil to prevent it from running. (available from Aircraft Spruce and Specialty) Tape off the stab, fuse and saddle with blue painters tape. Apply the mixture with a Popsicle (craft) stick or a tongue depressor (craft stick) to make a nice radius. After it starts to harden a bit, you can smooth it out or shape it a bit with your finger dipped in denatured alcohol. Before it is fully set, peel off the tape. Let it harden. It will be smooth as silk and will not require any sanding at all if you have done it right.