I recommend storing the flue cover inside when highway driving. I lost the
OEM flue cover for my Westfalia somewhere on the highway many years ago. I
purchased a new one (big $$ for a crummy piece of plastic) and only use it
when washing the vehicle. I've never had problems with rain or critters due
to the flue being uncovered.

Roy O.
'87 Westfalia
(till death us do part)