undercoat floor

I have a Geo tracker that is in excellent shape and I wouid like to keep it that way. I want to paint underneath the carpet, there’s some light surface rust and that’s it. I wouid like to undercoat to help with the cab noise but will this actually seal and not allow water to get trapped? I’ve seen a lot of cars with undercoat that was peeling and very rusty underneath but I assume that was poor prep. Is there a better product ?
I know it’s not a Mopar but there’s a lot of expierience on this site.