From what I read, they get the trailers shipped to locations, and they'll be shrink wrapped and then stablized with big foam blocks which they just need to trash or recycle so good chance they'll be happy to get rid of them... found the mention!!
Scroll down to the fifth picture and he says he got all those great blocks from Tractor Supply for free!
Most craft places like Hobby Lobby will have some type of foam blocks or pieces but they'll be expensive for what you get.
Check with a place called Tractor Supply and ask about foam blocks they get from trailers? I've read about that on here in the past, and they sometimes give them away for free (so I've seen; they usually trash them). Should be close to the size you need if not larger.
Also check boat/marine supply places; I believe they supply REALLY large (white bead foam) pieces...
The board's software coding doesn't like the newer http links (the ones with the youtu.be designation). I usually just paste that one into the address bar to go visit it and then copy the resulting longer address to use on Halloween Forum.
So using your example:
I'd go to https://youtu.be/RLJ_9id2yik, and once on that page, I'd see the following actual address in the web browser:
Copy THAT address and paste it into the