Do you have a real RUBBER bed mat, or a plastic one? If your bed mat was shiny and tended to hold the rolled-up shape when you cut the packaging off, it is PLASTIC. A flexible rubber-like plastic but plastic nonetheless.
An actual rubber bed mat is dull and flops out flat without having to leave it in the sun for hours, when you cut the packaging off.
I've got one of both. An old DeeZee from 1997 that is rubber, and starting to dry rot after all these years. That's the one that I use under my camper. My other one is a 2016 bed mat from Tractor Supply that is plastic that I use in my daily driver. I have no doubt the camper would slide around on the newer bed mat like a skater on ice.
Campers slide around on plastic, and stay put on rubber.
