No problem if the guy wants poly for sure give it to him I totally understand just if the caps break it falls on you so that's the worry I would have. Just pack the heck out of it to protect the caps that is what I would do to be safe. The foil 4oz caps or paper caps come from
https://www.sks-bottle.com you can buy a 144 or a thousand depending what they have in stock at the time. You just need to know the size cap for the bottles have, it should be a 22 or a 24 size cap. The bottles I will need to look at the place I got my last order from it was around $100 for 160 4oz Boston round bottles the Wheaton brand good ones.
The reason the lure makers I deal with like the 4oz bottles is it's easier for them to have it measured out and for me if I break a bottle I lose 4oz of quill if I drop a pint bottle I lose all of that then.
Paint cans are the ticket oil dry, kitty litter, dust dry dirt or sawdust all work well, I wrap every bottle in newspaper like the way lures come from a supply dealer to cushion them. Then I seal the lid with a paint primer in the threads on the plastic "cans" and the metal cans I put primer/paint in the lid groove then tape with duct tape once it's sealed. It sounds like a lot but a lot is on the line with the orders fate and the liability of the damage that could occur if it all goes bad.
Just know I was not trying to bust your chops in any way just thought the clarification of the options might be helpful to everyone that might be interested. The thing about essence is once that genie is out of the bottle it never goes back in the same way. LOL
I will find that place and get back to you I hope it's on the cases in the shed but they are shipped from the factory but I might have some paperwork in the boxes. If I can help you in any way just let me know.
Jerry