ProFlex RV sealant is not a silicon, but a solvent based caulk that they claim sticks to anything. I used it to seal the vertical seams between the aluminum siding and the vertical corner molding. If you keep a little bowl of mineral spirits handy, you can dip your finger into it and tool the ProFlex, creating smooth pathways for the water to follow.
The vertical seam is important, but since water wants to obey gravity, it isn't as likely to get in behind the vertical corner molding.
The roof is convex, so water is going to travel down the side of the horizontal corner molding and straight down the side and down the gutter. Note that if I had not trimmed the vertical corner molding where it went up and over the roof, the water would be obstructed on its way off the roof.
