I think mice contribute alot to the rust outs in these old trucks, they urinate and crap everywhere in them. The only places I know of on a new or good TF cab that they can freely enter is the cowl plenum drains, and if they can get up there the cowl vent grill. It seems once they are in there they have no problem getting into the bottom of the seats, all through the plenum and heater, and into the glove compartment, and in between the roof and inner panel, once they pack in the fluff and it holds the urine and other moisture the rusting begins.
