What would “best inner bags” mean, just the quality of the bags or something more? Well, since plastic side cases very often have irregular inner shape, in my opinion, optimal space usage is as important as the quality. Instead of the further explanation, let’s see the internals of the BMW touring cases:
BMW offers good quality inner bags but according to the pictures and forum’s opinions I could find online, they do not occupy all internal space. This can be good in case you want to add some additional items like rain clothes, but these small items may also very easily fall out of the cases when you open them so my conclusion is that it is better to use the whole internal space of the side cases by inner bags and keep all small items in the top case.
By searching online I could also find some bags with an external pocket which allegedly occupies the cases very well, but this is actually not quite true. It maybe uses more space than the original bags, but still the shape of this external pockets has nothing to do with the shape of the side cases. It is far away from occupying the whole available space. Besides that, the ones I got smelled quite bad and the quality was actually not that good as claimed.
Finally I got these bags:
As you can see on the pictures, these bags are shaped very well in order to occupy the internal space, the quality of materials are great, there is no bad smell, zippers are made by Held and so far I simply claim these are the best inner bags for your touring cases either for K1600GT/GTL or R1250RT. If you share my opinion, you can get the bags from Kleinert .