I'm talking more about the act of scoop shoveling mulch out of the trailer, constantly running scoop shovels along the floor and pulling them out. Standing outside the trailer, not in it. I wouldn't want a rough surface! it's nice to have things slide.
And, yes, mulch would probably dump out just fine. But what about topsoil? or wet debris? OR leaves??? I box my dump trailer for leaf season and when its full of 10 yards of shredded leaves, it doesn't always want to come out. If you leave them in overnight or they are wet, forget it- they'll stick right to the surface. Don't think line-ex would be good.... Besides, dump trailer floors are supposed to take abuse! You're not really adding valuable life onto the trailer by doing it. Why don't all dump truck drivers line their dump bodies with it? Cause stuff doesn't want to come out!