Great question — answering as the UphillTech team:
It is possible to have two tag manager tags, but this won't do what you want (and might cause problems). The reason GTM should be placed directly after the opening body tag and not inside another element is that GTM does a bit of DOM manipulation to insert the included tags. All your configured tags are packed into a Javascript object which is inserted into your page and fired from there. Putting the GTM tag into another location will not change the place where the tags are inserted (unless the user has disabled Javascript in which case image tags will be displayed in an iFrame). However it means the GTM tag might fail since the DOM operation that injects the Javascript might not work from...
Full answer by Eike Pierstorff: https://stackoverflow.stackexchange.com/a/24321943 (CC BY-SA 3.0).
Need it done for your business? UphillTech.
