I know just the thing. I used this method as a kid when we moved from Texas to Colorado several times because of my Dad's work.
First, get several larger sized boxes. 3X3' is about right.
Second, get some upholstery thread (heavier than normal threads).
Third, clear packing tape. (Post office or packing places.)
Fourth, layer the bottom of the box with polystyrene packing peanuts or foam rubber.
Fifth, put down one layer of finished kits. then around the outside of the box measure 3-4 inches above the foam at the bottom of the box.
Sixth, take a heavy gauge needle and sew the thread from one opposing side to another. When finishe you will have a tight grid of thread able to support the next layer of kits.
Seventh, add packing tape to the outside of the box as this will keep the thread from digging in to the holes and going slack.
You should be able to get 8 - 9 layers of finished kits in a 3X3' box. When unloading empty the top layer and snip off the emty threads to get to the next. Just don't set anything on top of this box except other similarly packed boxes of models. I usually averaged less that 5% damage over-all.