I think in the early days of slide outs or as called by some Tip Outs, supports were common. I think present day setups are better engineered and stronger and no longer required. Now if you are setting on blocks under the frame, I suppose you could add some additional support to the slides without any worry.
Michelle & Ann
2018 Chevy 3500HD Crew Cab High Country DRW, D/A, 2016 RW39MB, Dual ACs, Auto Level, Auto Sat Dish, Stack W/D, King Sleep #, 17.5" Sailuns w/Disc, MORryde IS & Pin, Comfort Ride Hitch, 5.5 Onan, Res Fridge & Induction Cook Top