You can do what you want, POR will work on all metal but it's really not designed for fresh new metal (and not required IMHO) but lots of guys use it. But lots of guys use bedliner incorrectly too (hint it's not a rust proofing product).
From their own website:
Surface preparation:
Rusted surfaces are best; seasoned metal and sandblasted surfaces are also good.
To coat smooth metal surfaces: Use POR-15 METAL-READY to prepare surface before painting. Surface must be dry and free of grease, oil, or other foreign substances. Use of 'rust converter' products is not recommended as they may affect bonding of POR-15 to metal. POR-15 likes to adhere to surfaces with 'tooth' rather than smooth, glossy surfaces.