DON'T line-ex it! Sounds like a great idea but, yes, the material will not slide out. You want that floor nice and slick! I would hate to imagine shoveling mulch out the back of a dump trailer with that coating on the floor.
Nice trailer! You will love it, if you have not had one before. Couldn't do without mine. Just saw the guys at my old job sandblast an old Bri-Mar last week and repaint it. They actually did line-ex the exterior and top rails. Looks great (but it is a black trailer.)