What will stop the rusting on the lower panels of 2004 Chevy Venture van?

Once rust has started, it is better to remove the panels and replace them with non rusted panels or new ones. Have the panels painted with a rust prohibit-er paint coating. Make sure the other metal parts around the front panels are also rust free. Either remove/replace the parts or remove and protective coat the metal. If you live where salt or other corrosive material is put down to melt ice, it will continue to cause rust. Try to keep the dirt and snow/ice from forming and sitting on your vehicle. there should be drain holes to allow the water to drip away from the inner panels. Use a car wash as much as possible. Once the application of salt/road additive is stopped and the roads are dry, get the vehicle washed and pay attention to the undercarriage. Some people will tell you they can fix the panels with car body repair bondo, but they cover the rust and it will continue to rust under the paint and bondo covering.