There are dozens of sound deadeners. Make sure nothing you use harbors moisture and on that topic, please let me suggest something else. Remove your doors and buy some oil-based genuine enamel paint. NOT water based anything, but any color is fine. Make certain the paint you buy takes at least a couple of days to dry completely. Stand each door up normally and pour about 1/4 cup of paint in tilting the door back a bit so it runs right into the joint of the inner door and door skin. Let it dry. Rotate each door and repeat, making certain each joint is completely full of paint all the way around (by continuing to rotate and pour in paint). Then with a brush paint the area all along the bottom inside (where the drain holes are). Even if you're just using your truck fair-weather style, you'll still wash it and after you've dipped those doors, the joint will be alarmingly susceptible to rust...and rust once it gets in that crack it can completely ruin a door before you ever know it. The best of all worlds is that joint is sealed so that no water can be held there. Good luck!
