The only way to get PayPal to insure your item is to send using a method where the address destination is noted on the same document as the tracking ID. Try sending using signature on delivery type post method. And ask your post office for a lodgement form. It's a pain but at least it shows where you have sent the parcel to.

Sending by prepaid satchels is not good enough to satisfy PayPal requirements. Check the fine print. This is very much stacked in the favour of the buyer.

The other thing you can try taking a picture of every parcel that shows the address labels and tracking ID in one shot. When a buyer claims of non-delivery then you could send the picture to PayPal. It might work.