Hi, new here. I am Karl Mullendore, the US rep and importer for Propex. I like to see that folks don't have any issues with reliability of these heaters, even if they didn't buy through the US delaer network.
Regarding the Propex HS2000 installation manual, it states:
"A 0.75 metre length of 22mm flexible stainless steel tubing with a special
end cap is supplied for ducting the products of combustion away to the
edge of the vehicle. The tubes may not be shortened but can be extended
for certain applications. A 0.75m length of combustion air pipe is provided, which is also fitted with
an end cap. This should be attached to the heater with the hose clip
provided and pointed in the same direction as the flue pipe.
Note: The combustion air pipe can be terminated underneath the vehicle
making sure the end of it is at least 0.5 metres away from the end of the
exhaust and that they are not pointing directly at each other. Take care to
ensure that both pipes have a slight downward slope to prevent any
possibility of water traps. Make sure that neither the flue or the combustion
air inlet pipe are terminated in an under-floor box section."
The reason being that the Omron airflow sensing device senses reverberation in the inlet and burner pipes, and when they are cut shorter than the supplied length the sensor may detect uneven pulses in the burn and shut the unit down. You may get away with it at lower elevations, however at altitude we might hear you cursing the furnace because it will shut down with an airflow fault code. You may of course shorten the heat ducting to any length.
In regards to the Atwood vs Propex: the Atwood efficiency is 75%, resulting in an output of 9000 btu. Propex efficiency ratings are 93%, resulting in 9500 btu for the 2000 and 2211, 9700 btu for the 2800 model. FWC has not approached me for a bulk OEM supply price, they could be using a more compact and efficient furnace otherwise.
Can you talk about the noise level comparisons between atwood and propex. Its not practical for truck campers to terminal underneath the vehicle since that would involve penetrations in the camper and truck bed.