I did, used an Estes Eliminator kit for the fin can and nose. Turned parts down slightly on a lathe to fit the LT-125 tube. Flew great, but if you attempt a G80, be sure to vent the lower section or this will happen to you too!
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I'm not sure what you mean about venting the lower section. It looks like the fins broke off due to flutter. Not sure how venting would affect that. Are you saying the sections separated due to internal pressure and then the problems happened?
I'm actually wondering whether it might be better to make the fins conventionally, from something much stiffer than polystyrene, like maybe carbon fiber plate, and epoxy them to the tube. Or maybe plywood shaped into double diamonds and sheathed with glass. Maybe slot the outer LT-125 to give them more bonding area and some nice fillets. Should be less drag due to the elimination of the step at the front of the sleeve (and the larger diameter of the sleeve in any case). I reckon that step may be setting up a shock wave as it goes through Mach 1 that could be playing havoc with the fins.
An Enerjet without the fin can wouldn't exactly be an original Enerjet, but if it actually works, I'm all for it.
ETA: I tweaked the 1340 sim file that I found posted on YORF to eliminate the fin can and instead have c.f. plate fins of the same thickness. On an AT G80 SU, the apogee increased from ~4000 to ~4400 feet, with the max velocity increasing from Mach 0.98 to Mach 1.01.