RMH hypocaust heated bed questions

Hi! I haven’t posted in years, but as my life transitions back to homesteading (after saving enough $) my brain is rolling again with bad ideas.  I have almost a year to bring these ideas to creation and would love feedback on this one idea in particular: a hypocaust style rmh to heat a bed.

Firstly, Has anyone heard of this being done?

And secondly, can my rmh be installed below a raised up (4-6 ft) tiny cabin resulting in a rmh that does NOT exhaust downward at any point like a traditional rmh? Essentially, I’m wondering if I can connect the top of the heat riser directly into the bell with the help of a metal worker. I’m aware that it will probably result in a less efficient design due to a faster exhaust flow.  I might be okay with that bc I am planning on reducing radiant heat and directing most (all?) heat directly into a welded metal bell beneath the mass of the bed.  

Which leads me to the third question, has anyone successfully implemented a rmh that does NOT direct heat to a radiant source (I.e. an exposed barrel) but instead directs all heat to a mass instead? I’m a fire snob and I think it’s a bummer to have a radiant heat source in my bedroom without getting the wonderful glow of a fire, and would rather install a small fireplace at the base of a rmh chimney area instead of having a barrel in the room(hence putting it under the building) Additionally, floor space is limited so it would be better to have the firebox and wood splitting mess outdoors, and I think the barrel is ugly(which I know I can address other ways).  

Thoughts? And many thanks to the folks at permies  who have taught me so much over the years!  Best.

Bell systems often have the heat riser enclosed directly in the bell. There is no need to have a separate riser enclosure/barrel. If you want a raised bed on top of the bell, you would probably want some sort of baffle or extra thick material directly above the riser so you don't get a major hot spot. If you did want the riser out from under the bed, either for height reasons or to have a hot plate or instant radiator, you could make the bell space open directly off the side of the riser enclosure. Then, however you lay out the bell, have the chimney connection come off the bottom of the bell space.

The purpose of the barrel is primarily to get the riser exhaust down to floor/bench level so it can feed a comfortable seating mass. The bare, radiating barrel helps this downward flow happen. Your situation has no need of either of these features. You would definitely want a batch box rather than a J-tube for this setup, so you don't need to go outside to feed it every half hour while burning.