Anybody know about problems with rust in general or on the hood specifically for 2003 Ford Explorers?
I think your truck MAY have a 10/YR 100K warranty against rust. You should call your dealer to find out for sure.
Just to clarify–Your vehicle has a warranty against rust-THROUGH, meaning that you are covered if the body metal actually develops a perforation from rust within the specified time period. You are not covered for just the existence of rust on the vehicle. So, check the exact details of your warranty (sitting in your glove compartment, no doubt) and see how long your coverage lasts.
And, no, the Explorer is not especially prone to rusting on the hood or anywhere else–or at least no more prone than any other vehicle.