I have ordered a set of the slickers but I not sure where to place them.
Just put them over the scrape marks you're getting on the floor - probably near the ends of the slide.
If you're getting scrapes at other places, you probably have some dirt or debris trapped under the slide.
I've never personally done it, but on our rig if you remove all of the inside trim strips from the slide, you can slide it out past the wall. Trick is to get something under the slide to keep it from dropping. The last RV mechanic to do that used a 4x4 the length of the slide, resting on the top of the rails.
Then you ought to be able to give the underside a good cleaning,if needed.
al