How do I set the HTML element of a text field?
Have you tried Panels Extra Styles ? As per module page :


  Panels Wrapper
  
  Wrap your panes and regions with unlimited possibilities.
  Go HTML5! Wrap your content in the newly defined tags. Add custom
  containers and HTM
  
  Wrapper: Element
  
  Wrap any region or pane with one of several dozen tags, including
  HTML5 elements.
  
  Wrapper: Raw
  
  Wrap any region or pane with a custom raw prefix and suffix.
  
  Sample output after applying the wrapper elements on 1 region and 2
  content panes: the powered by block and a main menu.