[Harry]

Ohh, #*)(!#**
I really feel for you, I have been a bit in the same boat.

I know of another method, it is a bit laborous but it might help.
I was advized to do this when I emigrated to New Zealand, and volume to transport came at a premium!!
If you are sure you are not going to play for a while, why not remove the heads, so that the shells will fit all inside each other,which of course will reduce the bulk considerably, the heads can fit-in with the shells.
Otherwise, I would not know but I am sure that our other drum buddies on the forum will have some good suggestions.

Cheers, Harry

PS. Sorry I forgot to check what kind of shells you have, and assumed they were wooden, but maybe yours are fully impregnated with resin, so that you don't have to worry about moisture absorbtion. I should have asked that first!!