Some people have custom frames made with both sides visible. Best option is have it done with museum-quality glass to protect the cards from discoloration from the light. Best way to avoid mold is to not store it in a mold-prone area, or store it airtight if you have no choice.
If you're just storing them and not displaying them, the rolled tube works great. You can even get one of those special tubes for transporting rolled up large documents like architect's blueprints - they're made of hard plastic which would function like armor, and you might even find one that airtight, meaning it's also water-resistant. That would keep mold at bay.