On some F9 models, I notice a raised square feature just after the standard roof fans-what is it and is there a detail part available these days?
Cedarwoodron
That sounds a lot like a winterization hatch:
The real one is used to redirect warm radiator exhaust air back into the carbody, to keep it warm. It can be "turned on or off".
Ed
I suspected it was that- thanks for the confirmation. (Sigh) and another EBAY order coming up!