DISCLAIMER: I cannot stress enough that what works for me may not be what works best for everyone. This is a “take it or leave it” thing!
*originally posted in Nov 2013*
Beside oiling the crap out the underneath of the car, I often slather every bolt head I see with anti-seize compound. You can also remove the bolts for a good proofing. The way this works is simple: dirt that stores humidity accumulates on top of the anti-seize but leaves your bolts and threads shielded from the elements. A quick rub off with a rag removes it when you need to work on the car. It also works wonders to prevent verdigris on battery terminals and grounds.
If you’re afraid of bolts getting loose when using anti-seize, simply add a lock washer underneath your bolt. Otherwise, make sure that you torque your bolts with about 15-25% less torque than the usual spec as the anti-seize factor affects the usual torque wrench feeling. Alternatively, you can use silicone or grease as well to seal your bolts up, but it’s harder to clean off when you need to work on the car. Silicone also makes for a weak thread locker but it’s usually enough to prevent vibration loosening. A twice yearly repeat for the anti-seize or grease treatment is more than enough in most cases, silicone is more permanent. Oh, and don’t constantly remove bolts in aluminum threads as those wear out quickly!
In addition, I also use copper anti-seize on my highway tractor’s battery terminals. It helps to reduce and greatly slow the appearance of verdigris on them. It is simply a matter of removing as much exposure to air and the elements as possible. You can also use the same principle on grounding bolts. Since copper is a conductive for current, you don’t have to fear bad connectivity. Of course, you could do the same with conductive grease but I find the copper anti-seize option much cheaper to use. I repeat the process on a yearly basis.