Can't add a script without encapsulating div's?

I need to add a script to all the pages of my site - in this case, Google Tag Manager. This script needs to reside between the body tags and will not work if embedded in div tags. From what I can tell, adding a script via Sitebuilder automatically encapsulates it within a set of div tags - which then prevents the Google Tag Manager script from working. Any pointers? Many thanks.