That would be practical wisdom unfortunately with a limited floor square area relative to wall and ceiling you have a limited amount of radiation area.. the thermal resistance of the plywood allows higher water temperatures. So our water temp is around 140f and the floor is perfectly fine.
In an RV / overlander there is limited space so complexities as mixing valves, secondary pumps, more radiators at higher temps is all very undesirable.
In our case a large fin radiator 12"x 24"x 4" thick with squirrel cage blower is on the hot side of the webasto and then in series with the floor heat. So the floor part seems a bit lower temps because of the heat loss in the radiator..
Radiators are specified with engine coolant temp of 180 to 200 f , that is way more then a webasto can produce.. hence your 60.kbtu heater cannot produce that with temps of 140 to 150f.
The efficiency gain in " normal house" systems is that you can lower your boiler water temperature and thus the lower stack temperature hence higher efficiency..
None of that is archievable in a small rv / overlander setup. With 4 people and two dogs.
We run this system now for 4 years and it is ok, would I do again yes.... I am just warning the OP with some practical experience that it is not all sun and roses or something to that effect.
You can check out our build and adventures at skoolie.net search for "Dory"
Good luck, Johan.
