Hi,
I also use the large cushion for long trips. I found it to work better when i fit the insert upside down into the cover. It gives me a smoother surface to sit on. Just a personal preference as every backside is different. The straps are cheap and useless on the Ten. A couple of bungees work much better.
I am not going anywhere far without it anymore.
Try buying in the US, much cheaper. Just don't declare the real value, customs will screw you. (is this legal?)

Rob