What protective coat 4 underbelly?

My 83' Dodge Diplomat police package never had any undercoating applied to its chassis when new.
Now that it is showing signs of surface rust on the underbelly/chassis, I was wondering if POR 15 is still the preference or is there some other new advanced stuff out there that does not peel like POR does. My new tank is also exposed now, it looks galvanized though.
Thank you.

looks like everyone that has used Resto Ricks Zero Rust stuff is happy never saw anyone here complain about it. It can be brushed,sprayed and even think enamal hardener{like used in single stage} paints can be added

I will use some in the inside of my frame when the time comes
Resto Rick Site