[Graham]

If a stronger box means a bit more shipping cost but drastically reduces the chance of being damaged I think that's a fair price to ask.

Alternatively, individual small cardboard boxes for the cars with enough room for them to be wrapped in bubble wrap.

I think the idea of sending each of the internal boxes separately might work, I would need to cost that out. Of course it does increase the mathematical possibility of one or more getting lost in transit, then with the one shipment. But handling may be less of a risk.