I generally store my comics in boxes
They tend to wear over time, hosue moves, things like that, so I buy new boxes periodically
Bags and boards are important, I tend to do a change out every 10 years or so
For slabs, a sturdy cardboard box, or the box they've been shipped to me is well enough. I also tend to keep my slabs in the plastic bags they come with. Some of those bags are thicker than others, but I don't mind, bags tend to keep the scuffs down.
So far this method has worked for long term storage (10 plus years) but for each their own!