of excessive heat from the steel which could melt the plastics/acrylic so a consideration
would be a sealed waterproof fireproof box which are heavy and bulky.
It would have to be both fire and waterproof!
On the removal of the scratches I have some acrylic sheets which I have been
meaning to "scratch and remove" with the sand paper technique to post here but
I just cant get the time. maybe next week....
I can't imagine how heat will "ruin" the contents inside of the stainless steel box. Perhaps the plastic storage boxes that are waterproof, shockproof, and dustproof are a better solution? I own many unbranded small plastic boxes from China, but they often feel cheaper compared to the bigger ones made by Pelican (although these are much more expensive). If there was a plastic storage box with foam inserts for graded coin slabs (at an affordable price), I'd pick one up without hesitation. I might try sealing the coin slabs on vacuum-sealed bags for added protection. Wish me luck!
https://www.amazon.com/NOVUS-Plastic-Fine-Scratch-Remover/dp/B002UD0GGS
Works great on graded trading card slabs, which are basically the same thing.
Cool. I may have to try this solution on my PCGS-graded collectibles someday. Both the sandpaper and the scratch remover solution are cost-effective methods that don't break the bank.
That said, I appreciate everyone's suggestions. I'm locking this thread now as my problem is solved. Feel free to contact me on PM if there's anything else you'd like to add. Have fun collecting!