Interior rust prevention and sealers question

So I you haven't seen yet, I have rust in the interior and need to repair the rocker hole into the car. Now my question is how do I go about preventing rust from coming back since its already pretty aggressive but only at the surface rust stages.

What products do I use to remove the rust
I have por15 but having used it on my exterior I didn't like how it didn't stay on after a year and started growing rust again.... No idea why but was still surface rust.
Sound deadening material that's cheap and not dyno mat or as aggressive of a deadener.

Carpet is removed and want to ask what would you do with a small budget to clean up everything.

Here is a pic of the drivers side only for now as to what ill be dealing with.

Quarter behind the back seat speakers.

And the hatch area where the previous owner or one of them sprayed a rubber adhesive and plopped a piece if MDF to mount the relocated battery too.

Sand blast the surface rust, cut out the rot, coat everything in Por15 and then paint over that with hammered finish Rustoleum, which is tough as nails when applied properly.

New Guy":antcnawd said:

Sand blast the surface rust, cut out the rot, coat everything in Por15 and then paint over that with hammered finish Rustoleum, which is tough as nails when applied properly.

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I was thinking of Borg those things but I'm wondering if the rust is to bad already. Will it just come back?