I started thinking about how the tube material could be improved.
Although I love the ghetto look of pringles wrapped in the invincible duct tape, improvements can be made.
You could use PVC or ABS for the tube, it wouldnt need pressure rating because Im sure this thing wouldnt have enough power to explode the pringles/tape team.
This is rather cheap and you could just glue on an endcap.
Then a BBQ ignitor can be threaded in, a ring to define the chamber and barrel and fuel sprayed in!
However getting the perfect cost/durability/strength ratio is hard.