2011 Keystone Fuzion 405 Water Tank Support System Failure

It sounds like your tank was install just like every manufacturer installs tanks. That being said....exactly how do you "overfill" a water tank??? The water flows out the vent when full. I think what happened was the self drilling/tapping screws were over tightened and stripped the steel when installed allowing for the screws to fall out. Self drilling when installed properly are a great fastener