"very low" and "occasionally" suggest there's not much that can be done about it beyond the defensive measures noted above. Unless "very low" means Sagging. If it's old or driven a lot (and oddly, standing a lot), the springs could have lowered the rear a bit. If they're weak it'll bottom more easily than it should, sway more, and make it easier for one corner to dip into hitting bottom.
Is the coach level on level ground? If it's long rear overhang, common with rear queen bed floor plans, likely this is Nature of the Beast.