How can we have a contained GridBagLayout, with preferredSize, with vertical scroll only [on hold]

Does anyone know how to add a ScrollBars to Panel with GridBagLayout, with vertical scroll only. The panels components need to be self contained when the user resizes horizontally until a minimal size has been reached. Vertical scroll needs to be visible. I can add a scrollbar, but need the components to stay on screen and all visible horizontally. The GridBagLayout should still move the components.

The code:

import java.awt.; import javax.swing.;

public class SwingTest {

public static void main(String[] args) {

    final JScrollPane scrollPane = new JScrollPane(addCustomer());


    JFrame frame = new JFrame("Swing Test");
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    frame.setSize(640, 480);
    frame.setMinimumSize(new Dimension(300, 480));
    frame.setLocation(200, 200);
    frame.getContentPane().add(scrollPane);

    frame.setVisible(true);
}

public static Component addCustomer(){
    JTextField textField1;
    /***********************Initialize Fields******************************/

    JLabel labels[] = new JLabel[2];

    labels[0] = new JLabel("Left side - more components to add here");
    labels[1] = new JLabel("Right side - more components to add here");

    textField1 = new JTextField(10);
    JComboBox<String> materialTitlesCombo = new JComboBox<String>();

    materialTitlesCombo.addItem("-");
    materialTitlesCombo.addItem("test");
    materialTitlesCombo.setPreferredSize(new Dimension(250, 500));
    materialTitlesCombo.setMinimumSize(materialTitlesCombo.getPreferredSize());
    /****************************Create the canvas**************************/
    GridBagConstraints constraints;

    constraints = new GridBagConstraints();


    final JPanel panel = new JPanel(new GridBagLayout());

    constraints.gridx = 0;
    constraints.gridy = 3;
    constraints.gridheight = 1;
    constraints.gridwidth = 1;
    constraints.weightx = 0.5;
    constraints.weighty = 1;
    constraints.anchor = GridBagConstraints.WEST;
    constraints.insets = new Insets(-20,20,0,0);
    panel.add(labels[0], constraints); //Left side

    constraints.gridx = 1;
    constraints.gridy = 3;
    constraints.gridheight = 1;
    constraints.gridwidth = 1;
    constraints.weightx = 0.5;
    constraints.weighty = 1;
    constraints.anchor = GridBagConstraints.CENTER;
    constraints.insets = new Insets(-10,-9,0,9);
    panel.add(textField1, constraints); // TextField 1

    constraints.gridx = 8;
    constraints.gridy = 3;
    constraints.gridheight = 1;
    constraints.gridwidth = 1;
    constraints.weightx = 0.5;
    constraints.weighty = 1;
    constraints.anchor = GridBagConstraints.WEST;
    constraints.insets = new Insets(-15,15,0,0);
    panel.add(labels[1], constraints);//Right side

    return panel;
}

}