How to attach fins?

I've got a project that's been pushed to the side for quite a while that I'd like to get built. It's a basic 3FNC. The body tube is 54mm phenolic. Where I'm stuck is on how to best attach the fins. What makes it a challenge is that the body tube was made so that any of the three motor mounts can be interchanged (single 24mm, 3X 24mm, and single 29mm). There is a thrust ring inside the body for the mounts to push against, and there are three #8 machine screws that secure them (through the body tube, from the side - nuts are built into the motor mounts).

This means I've got to mount the fins flush with the outside of the body - can't use through-the-wall mounting. I don't want any fancy/complex fin designs. Probably just a clipped delta with a long root. Am I over-worrying this? Will probably make fins from 3/16 ply, and glue them on with yellow glue and add epoxy fillets. Should I lay down some glass in the fillet as well?

What airframe material? My limited knowledge tells me to attach the root of the fin with epoxy and use Thick epoxy fillets. Possibly with chopped glass in it. If you are using paper airframe, you will be fine tacking it down with wood glue and doing epoxy fillets as you said.

I'm not sure I would trust wood glue on phenolic. Just tack them on with some epoxy and give them some nice fillets and you should be ok.

Two options come to mind. The first is to glass the fins tip to tip basically making a fiberglass fin can. The second would be to use tube fins.