Rocket Mass Heater \ Radiant Floor combo

I was thinking of doing a small "Hard Tent" super-adobe structure with about a 10ft radius with a hex roof with a rocket mass heater and bench. It occurred to me that I could put in some radiant heat flooring and do hot water by coiling around the RMH's drum exterior. I was figuring about an inch clearance would be sufficient for picking up the heat or would it make more sense to run a pickup line through the bench itself to draw the heat? I don't know if I can run a coil inside the drum as I'd have to worry about boiling the water in the coil then having to address the pressure in the line. Anyone who's done hot water from the RMH know a good heating rig to use to drive the radiant floor?

Erica Wisner started a thread on this very topic. It doesn't matter for what purpose you want to use the hot water, just how to heat it safely.

https://permies.com/t/34547/rocket-stoves/Rocket-Hot-Water-SAFE