I ran into a similar problem on my Eagle. I initially installed the Maxxair Fan/Mate cover, the problem was it extended right "over the top" of the stink pipe...not good.
Took it back and installed the standard Maxxair cover as shown below:
Just a little tip...., if your bath vent fan is a high speed unit, remove the fine mesh screen from the the Standard Maxxair (if you use it), it will reduce the back pressure when the fan is in use.
Bob
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2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)