exactly why my trucks have no carpet and spray on bed liner inside & out. also why I moved the dimmer switch to lower edge of dash by hood release. water would short out/rust the switch and it burnt up the fuseable link wires on 2 of my trucks. took a while but I found good replacement wire harness for the 85/88 trucks & moved the switch to high ground.
couple well placed 1/4' holes to drain floors well and it stays dry and a little damp in wet weather but dry's right up dry weather.

IMHO..they all leak no matter what. so drain it well and ride the wheels off before it rust away.

OH yea, windshield gaskets leak also. mine leaked and run water down the a-piller and then down between dash and kick panel to the floor.
cargo light leaked and run down inside cab and keeps seat belt wet and rotting in the bolt area.