SV,
If 3 adults are on one side it does tilt down a bit but it doesn't seem to come anywhere near close to wanting to dump you in the water. If you have 3 or more adults on opposite ends you will notice a slight bowing in the center (a result of the center row of barrells?) but as I said it is very slight. It seems pretty stable to me. I also screwed in a 2x6 on each end between the stringers to keep the barrells from rubbing on the carriage bolt ends so the barrells are about 8 inches or so in from the 2x10's. As a result if one adult stands on the very corner it will dip enough to get the wood wet. I can't think of any other way to keep the plastic barrells from getting abraded on the bolts. I hope this helps. If you think it would be of any use I could get a close up picture of the screw pattern on the decking to show the position of my stringers.

PETA, People Eating Tasty Animals