Hi Toby,
My suggestion is, in case of a lot of bases, to buy 33ltr Really Useful Boxes, At first they look huge but they offer enough space above the pikes, flags and Standarts and for about 50+ 6x6cm bases inside. I use magnatic self adhesive sheets inside the boxes and Flex Steel on the bases so they dont slide around.
As I travel with about 10 or more boxes of this type each year from Austria to England I can confirm that not one Miniature has been damaged.
Here is a picture to show you how this works
Hope that shows you an option.
Cheers,
Günter