Can the money in the storage be plundered too?

Any resource items (those that you have in the items menu) cannot be plundered. If that is what you mean by storage. This includes money.

Resources shown at the top of the screen are active and vulnerable. Other players can attack and plunder food, fuel, timber and iron. Players who are the Raider class can also plunder money if they use their class APC to attack you. But only from the active amount shown at the top.

If you are a Farmer you will have a depot protection that will keep a fixed amount of it safe.