You'll be able to see them clearly and they won't get cold.
Bedding is very important, it needs to be soft and warm.
You can buy gerbil bedding or give them clear paper tissue and small boxes to chew. You can cover the bottom of the cage with saw-dust, cat litter, try peat, or sand. If this is deep enough your Gerbil can make tunnels in it. Clean water should be given daily in a bottle, not in a dish. If it is in a dish your gerbils bedding and wood shavings will get into the water.