Correct. For the levelers to work properly the unit should be leveled FIRST, then the slides out.
If not, the unit will get level, but could end up higher than need be. If the unit leans due to the slide, it could set the level off the high side first, which brings the low side up, instead of the high side down.
PLEASE do not send questions via Private Message, my inbox fills up too quickly. Post questions in the forum as a new thread so that other users can benefit from the answers. Use Private Messages for sensitive information only (VIN, Contact info or things you do not want the public to see).