There is a difference between a MH frame and a trailer frame that greatly affects the frame twisting when out of level. A MH frame has the wheels on 4 corners, trailer frame has wheels near the center.
This means the slides in a trailer frame are only slightly affected by an out of level condition. So, IMO extending trailer slides has a slim chance of damage when unlevel (overnight stop),
With todays RV refrigerators, unlevel means you are uncomfortable living in the RV-sleeping, walking, etc. Running the refrigerator is the major reason RV's should be leveled, the comfort factor just means the frig is probably level enough for safe operation; which is 3 degrees side-to-side and 6 degrees front-to-back when looking at the frig door.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert the Constitution. "Abraham Lincoln"