The golden rule for storage is: Slabs (and mint-packaging) are for chumps. Real collectors crack them out and throw them in a pickle jar.
I never thought about it, but the only way to know the difference between pvc and pvc free flips is to have each in your hand. PVC flips will feel like a shower curtain, and be very pliable. It feels like you can bend this back and forth forever. THey are used since many people may handle these coins, and they should bend freely. Pvc free flips feel hard, like the edge would cut you. They do not bend well. All around they are worst products EXCEPT they will not leave a residue on your coins, which is the entire point. Please everyone, always know what kind of flip you are storing your coins long term in.
These storage bags are awesome. I've used them before. I think NASA and some other big names even use the anti-tarnish products from this company. https://www.interceptjewelrycare.com
If silver coins are stacked in a tube, I realize that they will likely scratch each other. Can I put them in a tube, layering them with cardboard spacers to prevent that?
The honest answer is not what anyone wants to hear. No matte what environment you store a metal like silver, it is a noble metal and will even in an airtime container eventually tarnish. Airtight container with a base environment will yield the longest sustainment of the blast white as you. An hope for. In today's market, you dont want to prevent toning, you want t to take place in your lifetime so hat you can take advantage of he hefty premiums rhat all these monster toned coins are going for.