1.) there are two drain holes above the firewall on either side of the fan box---be sure to keep these from plugging up or you will have major structural rust issues 2.) when lifting the truck or having it lifted, be sure it is not lifted under the doors at the welded rocker/floorpan seams. when these get crushed, water gets past the compromised seam and the floor pans get rusted out. 3.) check under the windshield on the driver's side to see if water is leaking from the windshield seal. A leak in this area usually finds it's way to the fuse box and starts serious problems. Leaks are common in this area after many years.