If you search the forum for “water leak” you will find several threads. Silicone should work, I used RTV. You are sealing the bottom of the rain gutter which will not be visible. The one exception is the seam at the end of the rain gutter where it angles down to the hatch. It’s postulated that this is where hairline cracks develop in the weld allowing the leak. I pulled our rack & examined everything carefully but was never certain where my leak actually was. I over did it & just RTV’d the weld line along the entire rain gutter & the area in back with no more problems since (2 years now). As you’ve surmised, here in Puget Sound it rains almost daily starting in October and going up to the 4th of July - doing it now is a good idea.