Transporting large pottery 1,500 miles SAFELY!

Hello ,

we are in the process of moving 1,500 miles. I shall be moving some items on a trailer and want to take our large ceramic planters and have them arrive safely. I am perfectly capable of building a wooden frame for support, but its what will be underneath that is most important to me.

What type of, and how thick of a foam would you suggest for transporting these ceramics safely? The largest is 4 feet high and 3 wide and is a tussle fora single individual to handle ( empty).

Thanks in advance,

Gene so