Thanks Liz, you are my new best friend
To clarify for others the following goes in the second half of the tabs.tpl file:
Please note that your first extra field would have [0] in it, here [2] is my third extra field.
<div id="tcontent12" class="tabcontent">
{$extra_fields[2].field_value}
</div>
Easy when you know how but frustrating when you don't.