[EdenSlate]

A video of me putting the item in the box, sealing with tape, applying the label, could be a proof to keep and sumbmit to paypal in case i need it (of course i will empty again off-video ahah)

That could be nice to emphasize you're acting in good faith, but probably unnecessary.

also read here of people that do this with a small envelope, but a bit more risky i think.
I don’t find feedbacks for empty box here instead (heavy items)

If you're expecting PP to disregard the company's potential answer & refund you, maximize your chances of success : match the weight.