Hi Dave,
Welcome to the forum, to select multiple containers for your single page:
Add a text / HTML module to a page
Go into the module settings menu for the Text / HTML module
Click on Page Settings
Under Basic Settings is Module Container
Select the container you wish to use here
Scroll down and click on Update
Add a second Text / HTML module to a page
Follow the same steps above but select a different container
You can select a container for any module on the page
This tutorial should help to make it clear how it all works:
How to use Skins and Containers in DotNetNukeHope this helps, thanks,