When I see any repairs around a vent I follow a rule, take it out and clean it up, do the install all over again with the butyl tape, reassemble after cleaning all surfaces with soapy water first, after it dries up follow with an acetone wipe off on THE TRAILER HULL ONLY....Acetone can dissolve some vents!!!!
Silicone/Urathane blends do work when formulated for fiberglass, but
do not disassemble well and the tape will, the screws are important too, a dab of "Goop" (brand name) on the threads will stop leaks
here too which is so often over looked in fan installs.
Happy Camping, Safe Trails.