Thank you for writing about the pot for your fig tree. We do not recommend putting anything in a pot other than a good potting soil mix. Any other material will disrupt the drainage and may cause root damage. Here is an article that explains how drainage works (or doesn't work) in pots:
If your container is too large, I suggest planting the fig in a smaller, appropriately-sized pot and then placing that it the bigger container.
If the container is the right size for the fig, you can buy a plant trivet on coasters to make it easier to move. Make sure the container has several drainage holes in the bottom. It should then be elevated at least half an inch above the drainage dish underneath the pot.