I built a portable RMH in my shop, as a test for eventually building one in my house. I came up with, I think, a good idea for the container. I built it in a metal stock watering tank, 2'x2'x4'. It's a 6 inch system, and works very well.
Some things Iearned:
I found clay pavers for 20 cents each, about the size of a firebrick but not as thick. I stuck one in my woodstove for a week and it came out with no visible damage, so I used 'em for the burn tunnel. So far, after a dozen or so burns, they are holding up great! Much cheaper than firebrick.
I started trying to stack up the pavers to create the exhaust manifold, and then realized I could just shape the whole thing out of clay. This isn't a new idea, but I had no experience with clay or cob so was hesitant to proceed that way. Once I started molding it, I was laughing. It's sooo easy and fun to shape with the clay! I'm just wanted to encourage anyone who is thinking about this to just go ahead and do it. I dug up clay from my property where I thought previously there was none, and just went for it. It's a blast, and solved a lot of problems I was having a hard time with in my head. So yeah, just do it!
I used 5 six inch elbows to make the exhaust spiral up from the bottom of the stock tank to the exit, then back filled with clay and rocks for the mass. It works great, there's a good sitting area on that end of the tank, and the barrel throws off a lot of heat.
So, it's a self contained unit that has a 2'x4' footprint, and a metal housing. I think one could build one of these and set it on something to protect the floor, and run this in just about any location. I'll get some photos up soon.