If for some reason you can’t display your shells, you can only put them in plastic boxes. I suggest cotton wool to put the shells in and wrap the shells with kitchen paper towels.
Don’t wrap any shiny shells with paper as it can damage them by the paper absorbing humidity.
Trust me, it will damage Cypraeidae, OIividae, Strombidae and Marginellidae. I have damaged about 10 large Cypraea caputserpentis and other species in this way.
It is good to put some humidity absorbent bags in your sealed boxes.
Shells are sensitive to sunlight, it will bleach their colours after a while.