Many, many years ago, my grand parents had a 35 footer that they would haul to Florida every winter. They finally purchased a park model and sold the 35 footer. The people who bought it came back to them about a month later and said they were having problems opening and closing the doors. Grandpa went over to their seasonal site and found that they had raised the camper off the ground using cinder blocks and pieces of wood in the four corners to get it level, which caused the camper to bow in the middle and make the doors out of square.
After putting some support in the middle of the camper, things were back to normal for the new owners.
All that being said, I will never forget that story, but I will confess, if I can't get my camper completey level using blocks under the tires and tongue jack, I will add a little extra pressure to the corner jacks to get me as close as possible. Im have a little ocd about how my camper is placed on a site, and how level it is. It might take me an hour or two to place and level my camper correctly