I too use the Marshall Brass Extend-a-stay.. Alas, they no longer make them.
There is one common issue I have read about. This is easily fixed. I do not know if it the tank or the adapter that has an excess flow valve,, If for any reason there is no pressure in the lines, and you have enough line. then when you open the main tank valve this excess flow valve will seat and shut you down.. The solution: Turn off tank valve, Enjoy a cup of electrically brewed coffee.. SLOWLY open valve till a person with good hearing just hears gas start to flow.. When they can no longer hear it, open a bit farther, and farther. Till it is fully open (never leave it partially open for more than a few minutes).
NOTE: the Extend-a-stay should not affect flow to furnace or stove. (or anything inside the RV) unless that excess flow valve slams shut.
Flow to the grill (or from an external tank) however MAY Be restricted.
Folks with "Monster Grills" often report low flow issues.
And though I doubt there would be low flow from a portable tank with the gas coming out at around 200 times the pressure delivered to the furnace.. I can imagine it could happen.
