I have a bubble bum for the occasional need for a booster in the middle of back seat of my BMW X5 (so narrow barely fits any other seat). I have been trying it out for my 6 year old as we are traveling to costa rica soon and I'd rather not pack a hard booster. We will be traveling on a small plane that only allows 30lbs per passenger in baggage so space is limited. We will be renting a car when we arrive at our destination so we need something for her. She says that she slips off the bubble bum and it slips out from under her. We do have the seatbelt threaded properly and when she's sitting properly it fits fine. Have any other kids here complained about it slipping? I have a feeling it's my leather seats. Our rental car will most likely be cloth seats so that might help.