danger of rust damage if roof antenna left off?

i've been leaving my antenna off because i don't really need it in the city, and it's a hassle to deal with at car washes.

is there drainage between the plastic base and roof? is there any part of the screw threads or roof contact that could rust? i live in rainy portland.

i've considered putting in a plastic screw to keep out water. unnecessary?

i'm sorry if a simple look over could solve this. i am short and i don't have private parking and i don't own a ladder.