Ready to Rust-Proof my Interior

I have pretty much stripped out the interior of my car to deal with some rust issues. I know that welding in some patches is necessary down the road, but I currently don't have the equipment nor the skill to tackle this 'properly', so I settled on getting PRE, Rust converter, and Rust Encapsulator from Eastwood for a solid 1yr temp fix.

I was planning on painting the entire interior/trunk area with 2 coats of Converter, then 2 coats of encapsulator. But I'm not sure how to handle the NON-rusted areas.
Should I sand/scuff Everything? (not to bare metal, I know)
Should I use Converter over seemingly good metal/paint anyway?
Or just the Encapsulator on the those areas?

What have you found to work best in your experiences?

Thanks, I will give the Scotchpad a try.

I already have all the Eastwood products I mentioned. Expensive, but supposedly top-quality, which is why I want to make sure I don't screw up my prep-work and application.

I guess I wasn't as ready as I thought. I still have to remove all the old sealer, which I'm learning is imperative for the process, since it's all rotted, crumbly, and apparently hiding rust along all the seams.

And I also determined that the current heater core had leaked at some point. I'm not sure what gave it away--the bypass setup, incorrect sealer (clear, silicone?) along the passenger floorpan, or the fact that the floorpan is all discolored and possibly repainted.

Also, can anybody tell me or post a pic of the proper sealing locations in the fastback trunk? Couldn't find in the shop manual.