I am working on adding new front steps to my house. I needed to cut away some of the aluminum siding and now I want to add j channel to the lower edge of the siding that meets the composite decking. I haven't been able to find aluminum j channel but the vinyl is easy to find.

I know painted plastic will peel off. Krylon makes the spray paint that bonds with plastic. If I spray the vinyl j channel with the krylon first, can I successfully paint over it with exterior latex paint?

You need to see a siding supplier, not the big box stores.