Is it my eyes, or are you also missing a tail pipe on the F150 also?
What, do you cut off your exhaust tips or something kid? Thats one of the ways how the beds will rust, is from leaky exhaust. Having no exit tips outside the body will just make the rust process happen that much quicker.
Ever notice an exhaust tip when the engine is running and moisture dripping from the end of the tip? Now imagine all that moisture coming out and getting under your bed. You are asking for problems, if they haven't appeared already.