If you need more that one design area per side, then you can use product fields (or design fields)
You can configure multiple design fields for each side of your product
Parts of the design that are outside the fields will be cropped
Options
You can also customize the field by setting various options such as the field label and the field type
The Field type shows these options
The Static field option will disable drag & resize for elements that are inside the custom field
The Limited field option will prevent the customer from exceeding the field size when resizing or moving the elements within the field
You can also configure text fields like this
The interface will look like this where the customer can directly enter the text into the corresponding field