Outdoor Thermal Seats

I have been researching the rocket mass heater for many months now finally feel comfortable to make my own. But yet I don't feel comfortable enough yet to put one inside my house for fear of screwing it up and hurting my family. Plus, my wife doesn't think they are pretty enough to bring indoors, especially with my lack of cob molding skills. I then thought I would put one in my greenhouse, but I don't really need the extra heat in there. So what was I to do .... then as I was freezing my butt off today during a surprise snow it hit me: Integrate the rocket mass heater into the new fire pit area I am making.
Has anyone made outdoor seats? What do you seal the cob with? What other material could I use beside cob? Could I make a wood frame, fill it with sand, and put wood on the sides and top?
How long is too long for the ducts? Could I run the ducts in one big semi-circle? Or must it pass twice through the same mass?
Are there any pictures of someone who has done this?
Thanks.

Kevin Mace : For a bit of something different try > Rocket mass floor heater - - finally completed and it works!(rocket stoves forum at permies ) Note you should
not be paying attention to the loooong Burn Tunnel, which requires Such a High Heat Riser (Xs 2) and outer Barrel/heat exchanger, but the split exhaust which no matter
how carefully you build will have a warmer section and a cooler section ! big AL !

Late note : pictures are on page 2 I THINK A.L.

Thanks Allen. I hadn't thought about covering the fire box. Perhaps I shall put it under the roof of and outdoor "kitchen" area.

https://permies.com/forums/posts/list/40/5937

Kevin : please note that this model has horizontal wood fuel feed,since this was made several D.I.Y. RMH, builders have worked to improve the performance of vertical batch loading RMHs
and their efficiencies rival the best Vertical feed J-Bend style Rockets, which are still the gold standard and easier and cheaper to build ! Big AL!