Been there, done that. I forgot to clip down the roof on the Nullarbor, lucky I look in the mirrors and one side had lifted, the other side was held by the awning thankfully. We had traveled about 10 to 15k at 80kmh so were very lucky and I became paranoid with checking the roof after that.
We did it today!! Left Bremer Bay and had only gone a couple of kms and our travelling companion saw it start to lift and flashed his lights at us. We realised that we had obviously forgotten to do something important. It was one of those days.. chucked the shower tent on the pack rack while the ute was packed. Went for morning tea with friends before we left and it was still sitting there foretuneately. No 3 event for the day is our travelling vompanions f truck gearbox just died so we are parked up til RAC can get here in the morning to take him home.