Sorry to be late to the party, but been away. We had oil canning last spring in a high wind situation. I crawled out of bed and deployed my speaker stand to very gently push hold the center of the roof up. I didn't press against the ceiling directly, but I didn't press against the rear lift bar either. Don't remember what I used to spread the point load. Anyway, oil canning stopped, sleep returned and had the presence of mind to take it down properly before bumping it in the morning.
Funny thing: no more oil canning the rest of the trip (about 10 days) despite high winds many nights. Could be wind direction relative to camper, could be window / vents open for ventilation, or it could be that I deformed (every so slightly) the roof so it doesn't do it anymore. If so, could be the roof was deformed from any number of minor mishaps (trying to raise it while still clamped, applying and removing flexible solar panels, hailstorms, bird droppings, etc) and that CAUSED the oil canning in the first place. Dunno.
Hope this helps.
Alan