AdvancedElements.com

Kayak: AE Lagoon 2
Backbone SKU: AE2023-DF2
Backbone Length: 109.5"

How should the backbone be positioned lengthwise? On this instructions video, it looks like it should be roughly at the rear of the tracking fin? Is this correct? When I purchased it, I though that it was going to be the size of the inside of the kayak from end to the other but it's substantially shorter.

https://youtu.be/DqDvosZbQeg?t=3m13s

The blades of the Backbone will fit just under the tube where it curves on the inside. When the tube is inflated, it pinches the blades to hold it in place.
The rear blade does sit just above the tracking fin.

Thanks a bunch for the quick reply This is what I've been doing but I wanted to be completely sure. Including a diagram along with the backbone would have been a good idea to help out rookies like me.

http://www.advancedelements.com/backbone.html

You can see from the diagram on the Backbone page, on the website, where the blade should be placed.
Same picture is on the box it comes in and on the instruction manual page included with the item.

It also explained in the tutorial video where the blades should sit.

https://www.youtube.com/watch?v=Ph3nPKx93Ig

Hope this helps