I built and fired an ill-fated overly ambitious J tube rocket that used a water cooled feeding tube.
The steel inner tube ran through the middle of a terracotta flowerpot that acted as the outer tube.
Both tubes were set in refractory cement, and the space between their surfaces was entertained with regular silicon caulk mixed with a paint thinner.
The goal was to keep tempatures down in the feed tube, allowing me to burn longer pieces of fuel without the draft reversing.
It worked, sorta, but there wasn't
enough water to keep the tube cool enough.
Plus, my riser had gotten wet, so it split asunder once it got going.
You could see the fire through the cracks, baleing wire held it together.
Good times!
Anyway, I bring this up as a possible way to make a water jacket barrel.
Inner barrel could be the top 24" of a water heater tank.
Outer barrel could be a 55 gallon steel drum.
Run self tapping screws into the space between the barrels, along their bottom edges, and pour a thick layer of fiber reinforced refractory .
Follow up with regular silicon caulk, thinned or not.
Regular silicon caulk is fine because 212 F is well within temperature tolerances.
With a band of refractory 4" thick, we could have a 20" band of water around the inner barrel and a 10" cylinder on top.