Don't forget about your mobile traffic. These people need some smaller popup campaign that fits mobile screens.
Mobile designs can be chosen when you create your campaign.
They can be modified just like any other pre made design..
You can stick mobile designs to any part of the screen.
TIP: you can set up mobile designs to appear on desktops as well. If you make them stick to some side of the screen, it can be a good way to display your offer and not to annoy your visitors.