After clicking the Clone button on a Soapbox Mailer Campaign, it's possible that your HTML Body and Text Body elements of your email are not copied to the new Soapbox Mailer Campaign. This is due to a limitation of Salesforce in that it will not copy fields explicitly included on the page layout.
While we're working on a more robust solution, here's a simple solution for the short-term.
1) Go to Setup > Build > Customize > Campaigns > Page Layouts > Edit link in the "Soapbox Mailer Campaign Layout" row
2) Drag a Section element to the bottom of your page layout of fields, and in the popup window that appears, for Section Name place "Clone Fields", and then click the OK button
3) Drag the Email Body HTML field, and the Email Body Text field from the top of the screen into the new Clone Fields section
4) Click the Save button
5) Collapse the Clone Fields section
Now, whenever you clone a Soapbox Mailer Campaign, the associated HTML Body and Text Body fields will be copied as well to the new Campaign.