The Sandbag for U tunnel is designed for the tunnel when it is curved.
Made of high quality fabric and resistant seams. Its triangular shape goes round the tunnel in a very effective way to keep the tunnel stable even with big dogs. 
Velcro-adjustable. It is detachable in 3 parts for easier carrying, and allows maximum adjust. 
Can hold up to 45 lbs in each side. 
It´s advised to fill them up with gravel instead of sand.