I will admit that I did have these for my Travel Trailer. It had a large 3' slide. But I was using this not to prevent "sag", but I was using to help stabilize my trailer. Again, this was a travel trailer with four corner stabilizers, and a slide that was a significant depth that caused a lot of weight outside of the jacks. I will say, in that case it helped a lot to reduce the movement of the trailer while we were in it.
Since I went to my new class C with a full wall slide, these have stayed in the garage at home. If you needed these to prevent sag of your full wall slide, I would be concerned about the build quality of that slide. Now if I was parked at a site for an entire season, I might bring them because I have them, but it would be more about reducing movement in the coach as people move around.
Thanks.
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