Seam Rust

[Foot Stomper]

Which seams are you talking about? Can you post some pictures?
To over simplify, rust needs oxygen and moisture to continue. Stop both of these and you have your solution.
Cavity wax has a fantastic ability to creep into impossible to reach places and will displace moisture and seal off oxygen and its easy to apply. It's a bit messy, drippy and doesn't dry and will attract dust and dirt. Even axle/bearing grease could be your remedy. Both of these options would be a far better solution and much easier to use than POR 15.