OK; Rust-proofing/Undercoating?

I used the dupli-color spray in bedliner in my ramcharger, the stuff is WAY better than any undercoating and is just over 9 bucks a can... did a floor pan in my valiant with it several years ago, the windshield leaks and while I was deployed it sat with water in it, NO rust. Pretty good bang for the buck... my two cents...