Ask people about that. I have used Rust Bullet, POR 15, and Eastwood encapsulator and I personally thought Rust Bullet was the worst to work with and POR 15 coming in a close last place. From my experience, an epoxy primer does a very good job as a base. I have used 3 different kinds and they were all very similiar, so take your pick. I have also found that Eastwood Rust Encapsulator makes a good primer base and comes in black, but does not have UV protection and would need a topcoat if its used anywhere but under the truck. It is kind of expensive, so a different epoxy brand might do fine. Here are some example pics (sorry not a mopar):
View attachment 1154707
The silver shown is Rust Bullet in silver. It had a tendency to not coat smooth and seemed to be a bit too thick. It may have good rust capability but looked bad to me (this is the bottom of a Triumph Spitfire). I stopped at these two areas and switched to Eastwood rust encapsulator because the Rust bullet was pissing me off on how bad it was to work with.
View attachment 1154715
This is after I topcoated with Eastwood Chassis black in satin. This wheelwell has a Eastwood Rust encapsulator primer in red under it (no rust bullet). It flowed much better and applied very nicely. For the record, both sides have prevented rust and look good for under a car, but I found the eastwood side was much better visually.
Also, the Eastwood chassis black makes a very hard surface and I find it repels dirt and rocks really well.
So, there you go, some real pics of what you are considering. hope it helps.
RGAZ