*Note that the fire doors at the end do not make a very good backstop.
I actually used to glued small balsa-wood fins directly to the engine to try to get some modicum of stability... with mixed results.
And I probably shouldn’t even tell about the “war-head” I once launched from Mom and Dad’s back-yard around dusk. With a hollow plastic nose cone filled with home-made gunpowder and glued to the rocket body, the “parachute ejection” charge on the rocket engine served as the ignition system. It didn’t go very high because of the weight of the powder but golly-gee what a BOOM and what a FLASH. That one brought out about 8 police cars and a helicopter. They even went door-to-door asking people about it. Fortunately, Mom’s response was: “What explosion?”.