You can print some of the backgrounds as banners.

For example if you used, they require 72dpi and that converts the 12x18inch 300 dpi to come in to 6.25 feet x 4.2 feet, 72 dpi So you can print at 4x6 foot banner. Here is a link to their requirements. I saw their products in person and they are very nice.

Another option would be to use the elements from the layered backdrops that you need for your banners and make your own design.

This is the video I did for someone else who wanted a banner that was a certain size and dpi showing how to resize it for a banner.

Additional Banner Printing Info:

This photo was shared by Lars Thomas and he said:

"As a customer, I was always confused about what size your templates would print too. So I can certainly see how this picture could clarify the issue for other customers. The posters in this case were 3'x5' - the resolution was fine, even up close."