I guess the idea is it protects the plastic underneath from scratches, but I agree, I'd want it anti-slip. Couldn't you adapt just about any universal mat?
I'd first get cardboard to make an exact template of the bed, and then use that template to perfectly cut to size a mat.
A razor, long metal straight edge, and spray lubricant should help cutting:
Granted there's the question of the hinge, but I would think you could simply make your own hinge between the two pieces you cut just using some kind of adhesive and a durable black cloth or other flexy material adhered on the bottom side where you won't see it, and either leave a gap between the two, or bevel the edges into a V shape so that when lifting up the brunk it doesn't meet interference. 👩🔧