If you're models are primarily of steamships, that makes it a bit easier. There's less to break and they are more compact in shape. Still, I would opt for tying them down firmly as I described rather than trying to "pack" them with any sort of material that is in contact with the model itself. More damage can be done to fine detail parts by contact with the packing material than anything else. The professionals first secure the model inside its case, then they secure the case inside a custom packing crate. You may have less to worry about if your cases are made of plexiglass, and if you are driving them yourself and, importantly, loading and unloading them yourself, you may get away without packing crates. Lots of mover's "blankets" may suffice. If glass, though, A plywood packing crate is required to prevent breakage for long-haul commercial trips. Since you've moved them before without a problem, it seems like it's only a matter of how much more work, rather than any change in procedure.