Rocket Mass Heater eastern MT

I need help designing a small rocket mass heater for our guesthouse, 18 X 20. Was excited to see Paul's video, that rocket mass heaters have made their way into MT.  See www.greenwoodfarmmt.org for our larger unit in our house/shop, it's working fine going into the third winter this fall.  Amazing this site exists, and all the interest! 

Do you have the rocket mass heater book?

Yes. The book was essential to designing our slightly larger variation, with open chimney-on-the-floor. I'm wondering about the strength of the pipe you used surrounded by heavy rocks/bricks. No crushing?  How do you fasten the pipe to the surrounding barrel? What's the size diameter and sheet steel gauge #  of the pipe? Maybe that's too many questions.....

No crush.

I think moving the exhaust from the barrel to the first duct is the hardest thing.  Did you see the long video version of the portable rocket mass heater?

Thanks Paul. I can't tell from the video if it's long or short.  It did not have footage of the attachment to the barrell, and nothing on the port through the insulation and two surfaces of the riser with the insulation in between.  I'm puzzling how to keep my vermiculite/sand mixture insulating the heat riser from leaking into the fire box.  My current system, in my 40X60 house, is welded steel 3/16ths or better, too robust to repeat in the 16 X 20 guesthouse. www.greenwoodfarmmt.org