Back in the prehistoric days before rocket sims... ie: late 90's ;-) I built what I called the Andromeda II. It featured a flattened hexagonal engine bay with a recessed, in-line cluster of 29mm-38mm-29mm. I fancied it looked a bit like the aft end of a Star Destroyer. The thick 38mm motor tube also formed the central tube (much as the 24mm does here), the crew compartment was a 3" tube with a custom nose cone. It did not have the diagonal conduits or the fin-on-fin antenna array. I detailed the Ram Jets to include stator fins and added a central 18mm nacelle but never powered them for fear of steering the rocket. No compression issues in the body and no issues with fin flutter although to be fair, they were plywood.
In this case, not shown in OpenRocket, I intend to paper skin the fins. I don't want to move away from balsa as I'd have no way to cut the curved fin profile in a harder wood, also, the diagonal conduits would be hardwood dowels much as they were in the original Estes kit. They are modeled in OpenRocket as extensions of the conduit mount but that was only for convenience.