The instructions with my motorhome said to level first, then deploy the slides.
If you have jacks, they make a solid connection with the ground, and is not subject to sway like when leveling with blocks under the tires, and the springs compress as you move around in the RV.
Level first, and you will not have any problems. It is no longer 'critical' to be super level. It is more for your convenience, than for safety problems, or the refrigerator needing to be level.
However you can not deploy the slides while 'way off level' as you might rack them, or bend something.
Also the refrigerator can be run on gas while driving, and the movement will return the ammonia/water mixture to the boiler just fine. But slow traffic, or parking off level can prevent the mixture from returning to the boiler, and should be avoided.
Back in the 80's a refrigerator needed to be very close to level to operate properly. Now they can be as much as 1/4" side to side off level, or 1/4" front to back off level. To be that much off level, the RV would be at a fairly extreme point, where walking around in it might become difficult.
Have fun camping!
Fred.
