Ship USPS Priority Mail tracked and insured. Works great with no BS.
This. No FFL required to ship through the USPS. Don't volunteer you're shipping a rifle in case a clueless idiot works your postal counter. It's not required and doesn't fall under hazardous material, etc.
I abbreviate any part of the business name implying firearms when shipping to an FFL and signature required. If you insure for a value over $500, the USPS automatically requires a signature at delivery, so no need to purchase signature required service if you insure it for over $500.
You can also separate the stock and barreled action to shorten the package length. Pack it like you expect gorilla handling.