- Thoroughly clean everything. Put on an extra coat of oil.
- Store in hard-sided airtight cases with foam cut to the shape of the firearms + scopes.
- Update insurance company information and check for accuracy.
- Toss big packets of silica gel dessicant into the cases.
- Lock cases.
- Seal cases with tape and initial over the seam of the tape.
I think we'll be using the same technique for other valuables like electronics, camera gear, optics, etc. Good shipping cases and insurance are expensive but the peace of mind is worth it.