Upload & Sell: Off
I got a couple "acid test" pens long ago with an order from Lightimpressions.com. Felt tips you mark on any material. Goes on yellow, turns blue if there is any acid. Your basic high school chemistry litmus test.
Used it on a box from Archival Methods. Passed. Used it on "white" boxes from UPS, Amazon, and the USPS. Also passed.
Acid free Archival Methods box, 13.5 X 19.5 X 1.5 = about $20
Acid free UPS box 16 X 20 X 3 = $3.85
Go to any local UPS (or Postal shipping) store for a wide variety of shapes and sizes.