Stop in for a cup of coffee

Good morning, retirees and the rest of us wanna-be-retirees...I was thinking just now. I used to have some Por-15 which I used in this way, is there anything else I can use (cheaper and I don't need much) to let flow into the space behind the trim of the back window of my Fury? Water collects there as we know and I would like to avoid rust.
I have used this as a temporary fix. Suppose it would do the job. My big concern with adding anything like this is trapping dirt and moisture and making it worse.
Permatex Silicone Windshield/Glass Sealer, 1.5-oz.: Model# 81730 | True Value