What type of grids do you have? If you have the mesh ones Flips shows in her photo I don't think you really need correx. Just line the ramp with vetbed or carpet tiles, fleece can also be used but may give less traction depending on the fleece and how steep the ramp is. If you have the "grid-grids" you can just put down cardboard, it will probably have to be changed, but it's not had to get hold of or expensive so not a big problem!