Gerbils need a lots and lots of bedding material. A very deep layer enables them to satisfy their nesting and tunnelling instincts. They need at least five inches of bedding on the cage floor.
As well as the bedding, you should consider giving your gerbils or nesting box - a house within a house, if you like. They like building nests in these. They will shove the bedding inside these houses, creating a space that helps them feel even more safe and secure. These house-nests also give them added privacy.
A snug little nesting box house in the enclosure will make an ideal Des Res for a Gerbil
Gerbils are diurnal, which means they’re usually awake during the day. However, those kept in captivity are likely to sleep whenever suits them, so will have several sleeps, both day or night, squeezing many 'days' into one. Allowing them enough material to tunnel means that they’ll have somewhere safe and dark to sleep whenever they’re tired.