I talked to a local dealer about them. This is the place that would make money if I bought some. They told me, that if the rest of the camper settled with a slide support down that it could damage the slide and/or its mechanism.
Ditto... If the trailer settles or shifts, particularly with a mechanical rack and pinion slide drive, it doesn't take a lot of upward pressure to lift the rack off the pinion by a tooth or two...even one tooth can adversely affect the opening and closing of some slides.
OK I just bought a new(er) fifth wheel that has a hydraulic piston drive slide-out (small slide, just the dinette). But I gather that a support is not needed under that either. Right?
Also... what do you recomment for lubricating the sliding bars?