[A/S] Roof vent fan covers

[Wayne Lindberg <waynelindberg@xxxxxxxxxxxxxx>]

Howdy all,

My '92 Excella is in need of new roof vent covers.  Without doing 
enough homework I bought a pair of Maxxfans, which appear to be 
functionally very neat.  They won't however fit my existing openings.  
Yup, duh.  So, I'm now doing the homework I should have done 2 weeks 
ago.

Has anyone installed these in an Airstream?  Is there anything 
particularly tricky about cutting the existing openings to accept the 
Maxxfans?  What goop should I use to seal the new adapter plate to the 
skin of the trailer?  The existing adapter plate has more rivets than 
there are holes in the new adapter plate, should extra holes be drilled 
in the new adapter plate to match the spacing of the trailer's rivet 
holes?

Any advice is appreciated.

TIA
Wayne