So what’s the correct way to level your rig without damaging the slides — before or after they are extended? The safest (and most warranty-wise) answer: “Do what your rig’s manual tells you. Here’s a lift from a Keystone manual: The recreational vehicle must be level to avoid binding the slide-rooms. Remember, stabilizing jacks are not capable of supporting the weight of your vehicle! They are intended only to stabilize the unit maintaining a level condition. Non-leveled conditions cause sticking situations providing damaging strains on the slide-out mechanism.”
This advice is pretty much standard with most RVs. If the rig is twisted, even a bit, it can put a real cramp on the slide-out mechanism. Pinching your slide-out can make for a most uncomfortable situation — particularly if you can’t “reel the unit back in” when it’s time to hit the road.
As to the case of the “leaning RV,” we can only say that if your rig leans after you deploy the slide-out, the most likely issue was not having your unit properly settled in the first place. Were the levelers on firm ground, or did they perhaps “sink” a bit into soft ground? Here’s a case for leveler or “jack boots” to provide a larger surface area to those little feet.