I live in Northern Ontario where the roads are heavily salted for 5 months out of the year. Drive a 1990 extended cab 4X4 that is solid as a rock.
Here's my secret , go to WalMart purchase a few tubes of their Tech-2000 grease (purple tube), it's cheap and extremely sticky , best grease I've been able to find for drip free home brew. Next get some cheap engine oil , even used stuff is okay.
Now sneak into the kitchen , borrow your wifes 300 dollar Moulinex processor/mixer , or if you don't want an instant divorce you could purchase a cheap mixer for 10 bucks at WalMart. Blend grease and oil into a thick consistent blend of goo , pour into a Shutz gravel guard gun (air operated) and proceed to spray inside frame rails/fenders/rocker panels/firewall/inside doors/hinge areas/ etc etc.
Rocker panels are very important areas , if your Toy doesn't have access plugs you can go to any automotive supplier and get some , drill proper size holes in door pillars and rocker panels , attach a hose to the nozzle of the gun ,spray liberally while moving the hose up/down/around spray the heck out've them , do the same into the frame rail access plugs.
This mixture is drip free and will last several years before having to re-apply , except in areas that are prone to heavy debris spray from the tires. I do the outside of my frame and underneath the box yearly.
My doors and fenders are original from 1990 , only have one little spot of surface rust beside my door handle.....not too shabby eh!.....and NO my truck is NOT for sale <img src="/forums/images/graemlins/smile.gif" alt="" />