we have the 21FBRS and we level it and chock the other side. X chock goes on side that is on levelers.
We sometimes use the other xchock but it depends if its under the slide and I feel like crawling under. For week long trips we always do i, because it makes things more stable.
2015 Ram 2500 4x4 6.4l with 2015 Flagstaff 21FBRS
Wife, myself and 2 furry kids