Keeping the lipos secure?

[StuartH]

I have just built my Cat K1 Aero and after jostling everything around to get the body shell to fit I have realised that my lipos rattle about!

I have a sort of core rc lipo saddle packs and I'm guessing with all the carbon fibre the battery straps are just a little too high for the top of the packs.

What do you put under them to get a snug fit? I was thinking of old bike inner tube cut down.......but surely there's another......and better way?