Nicely done. As an old rocketeer, the one problem with rocket tubes in that diameter is that the wall thickness is so thin the tubes are actually quite fragile. And yeah, the nosecone options are limited. But actually, a BT-20 tube (.740OD) with a balsa nose cone can be backfilled with two part expanding foam (go easy) to make a lightweight and durable airframe. The nose cones can be reshaped by spinning in a drill press or lathe with a sanding block. Hard points can be glued in before backfilling.

Slotting the tubes and gluing the fins in that way versus surface mounting will make the world of difference for durability. I'm sure you know already but don't forget to scuff the G-10 with a Scotchbrite or 220-320 paper to remove the surface gloss and any residual release compounds.