Your domes are quite small to heat with an RMH, but it should be doable if you are good at following directions and perhaps troubleshooting.
You would want the smallest feasible RMH, which for a standard J-tube design would be 4" internal system diameter. This size is known to be finicky, so I would test your construction before making it permanent. You could also build a slightly larger, and thus more reliable, version, 5" or 6" diameter, and just run shorter fires in it. Assuming the cold spells, and possibly occupancies, will be short durations, a smaller mass would be called for, as it will be more responsive to the firing schedule and warm up and cool down quicker than a massive system. I would not make shorter duct runs or smaller internal bell areas, but thinner masses that transmit heat faster.