Thanks for all your suggestions. I haven't had time to reply properly until now as travel arragements and final planning is taking a lot of time.
I decided to buy a cage that fits the bottle and attatches with velcro straps so that I can mount it anywhere I like, even on the top tube. IF I had not found said cage I would have used the aluminum stock method.
The more detailed reasons why we wanted to go with KK was
1) water capacity
I know we could have used the bladder method and we've used it successfully in the past. However due to weight distribution concerns and accessibility of water we wanted our water to be mounted on the frame as we're touring summer Europe and we'll be using a lot of water.
2) taste
As funny as it may sound, I used to get dehydrated quite easily when using plastic bottles because I could not stand the taste those things impart on the water especially if the water has time to warm up. As well as all kinds of leaching issues, which is especially nice when the leaching water container is going to be the only water container one uses for several months (this would not be an issue in usual day to day cycling, probably wouldn't be anyways, but I don't like the idea)
3) we could have used Nalgene bottles which impart no taste, but you can desinfect water in the KK's by heating the bottle. Unlike other metal bottles the KK can stand heating and you can boil water in them (althoug the manufacturer does not recommend it). A non issue in Europe but I want to use said bottles for northern bikepacking/hiking as well where drinking swamp water may sometimes become a necessity. And the bottles are steel and as we all know, steel is real
4) The clanking issue has not risen but as mentioned, it's quite easy to fix by using a bit of duct tape (or in our case gorilla tape)
5) option to carry beer/wine/other alcoholic beverages
6) wide mouth works like a beer pint which is a huge bonus
etc etc.
But again, Thank you all for your suggestions. I finally have this last kink solved (well, honestly there's still the issue of keeping my insulin pens and Glucagon cool on hot days, but maybe I'll have time to figure that out still...)