Guys, just to reassure you, I have had less loss with the envelope shipping than with small Priority flat rate boxes.
I have only lost one knife shipped in a padded mailer since I started in 2011, where I have lost or had stolen at least three small priority box mailers, in spite of sending many more padded envelopes. If the item is caught in the USPS machinery, no thin piece of cardboard is going to survive any better than an envelope. Anyway, that is my personal experience, and besides, they are much easier to ship, as Priority boxes have a habit of popping open unless securely taped.
Anyway, I will replace those lost or damaged by the PO.