To keep ice from forming in any freezer: don't place items warmer room temperature inside, make sure the items are well sealed so no moisture escapes from them, and don't leave the freezer door open.
Here is a link to the Refrigerators Manual:
For the maximum use of your freezer do not store excess
food. Do not introduce a large amount of unfrozen foods
that cannot be frozen within 24 hours (no more than
2 – 3 pounds or ,91 kg - 1,36 kg of food per square
inch of space in the freezer). Sufficient space must be
left in order for the air to circulate properly around the
packages. Leave enough space in order to close your
refrigerator with out difficulty.
Storage times can vary depending on the type and
quality of the food, the way its package, or packaging
container used, (in comparison to air and humidity), and
the temperature it being stored in. Ice crystals formed
inside your package are normal it indicates the air and
humidity inside your package have condensed.
NOTE: Let warm foods cool off at room temperature
for approximately 30 min, then wrap accordingly with
the methods mention above and freeze. By letting your
warm foods cool off before you introduce them to your
freezer it will save you energy.