The guideline says the box can not have any markings so I need to buy a box. I looked at the dollar store and they don't carry shipping boxes. The ones at Staples are multi packs and cost $$. I don't even know how to get reimbursed for them if they come in a multi-pack because the receipt is for the whole pack? Where are you getting your boxes with no marking and how to get them reimbursement for the one box if you buy a multi-pack?
For personal packages I sometimes open the seams of sturdy boxes with markings, turn them inside out, and use hot glue/packing tape to put them back together. If I don't have a box handy for a shop I'll do the same thing.
I would just wrap the box or, more commonly, use a piece of paper to cover up the markings. No clue why they have that rule. I wonder if anyone has asked about that in the main thread.