I built small rectangle frames out of 2x4 for my barrels to sit in. These frames sit perpendicular to the joust. You could also position the joust closer together so that the barrels sit on two joust instead of going inbetween them and hitting the deck boards. I'd think that the entire dock would sit too low in the water if the barrels were against the deck boards. You're gonna want the dock to sit off the water to allow for it to be loaded down when people are on it.