I have a lock n level for our Twin axle Delta RI, and it's great. I use a Michelin 12v compressor and it takes about 3mins to inflate both bags on the Twin version. I've used it at the Carsington CMC site for around 5 days and it never deflated. I was concerned at first due to the airbag taking the weight, deflating and then stressing the corner steadies as it it slowly deflates. I checked everyday both morning and evening and it was fine. You just need to make sure the valve cap is on securely otherwise air will escape. Until you unbox the lock n level, you don't really appreciate how robust, heavy and industrial it feels. With regards stones, I use those locking square sponge tiles under each and bag and check for stones. It's never been an issue. I don't understand how a caravan can roll off as each bag is much larger than the wheel and the tyre sinks inside the bag as inflates meaning it doesn't roll forward or backwards. If you require any photos or info, drop me a message. Chris