Answer: yes, you can stand with your flat-jack directly on small river stones and gravel campings. The flat-jack material is polyurethane, which is resistant to small river stones and gravel. Even with a heavy camper of 7500 kgs you can use the flat-jacks on these gravel campings. But we always advise our clients to prevent the flat-jack from a leak caused by too sharp stones, by putting a protective mat (floor mat or carpet tile) under the flat-jack. Between the stones there could be a piece of glass or a tent herring, so it is always wise to protect your flat-jack.