Truck unknown antenna base??

[AK9R]

I'm not concerned about a good-quality, properly-installed NMO mount leaking from the outside. What I might be concerned about is bare metal on the underneath side of the roof or trunk lid where you had scuffed away the factory paint to get a good ground. That bare steel would be a landing spot for condensation, depending on one's climate, and that would eventually cause some surface rust.

 

[mmckenna]

I'm not concerned about a good-quality, properly-installed NMO mount leaking from the outside. What I might be concerned about is bare metal on the underneath side of the roof or trunk lid where you had scuffed away the factory paint to get a good ground. That bare steel would be a landing spot for condensation, depending on one's climate, and that would eventually cause some surface rust.

I've never seen that be an issue, but like you said, it would depend on the climate. Not an issue around these parts. Certainly wouldn't hurt to do if you had the headliner down. It's pretty rare I need to remove the headliner when I install an NMO.