The temperatures generated in *any* decent
wood stove, and particularly a rocket stove, tend to be really hard on anything metal. So all those pretty pictures on the web have a major design flaw from the start.
The better builds will at least use clay to line the metal. Even some of the TLUD's I've read about are actually lined with clay. Our woodstove has clay bricks lining it, which we've had to replace as they wear and crack and then don't do the job, but the metal parts that can't be protected by fire brick, such as the afterburner, can get warped and have been replaced recently on the stove, but that was after about 15 years.
Some of the clay builds I've seen, will use metal or plastic pipe as a form, which is slid out when the structure has dried enough to be self-supporting, but not shrunk to the point of cracking. I say "clay", but I believe it's usually a clay/sand mix and sometimes there's a high
straw mix in the middle as both insulation and structural support, but I've not actually ever built one out of clay.
I did try once building one of the small tin can ones and was quite disappointed. A fire benefits from something "holding heat" such as the traditional rocks put around a campfire. I know I've read somewhere that perlite can also melt if it's too exposed, so that makes me a little wary also. My
experience may have been aggravated by damp
wood, but then I'm on the "Wet Coast" where there's a fire ban all summer and rain all winter.
I'm sure I saw somewhere a rocket made out of some terra-cotta pots, but I couldn't find it today with a quick search. I believe it required a drill with at least a masonry bit, although a drill press would be easier. It may have been called something like a "tandoor" stove - which is similar but different, if I've even got the right word. I will do some more looking. I really want a rocket cook stove, but there are higher "really wants" on my list mainly because I'd need a roof over it to be much use.