As a person that has lived up north all his life, undercoating is junk cash grab, POR-15 the underside all of it. Using motor oil any oil on the underside of the truck is not good for the environment nor is it safe for the people following you, if it sprays off and covers the windshield of people following they can't see.

Edit: You could look at a Mercathode system and use it on your truck or find a automotive style.

What is a MerCathode and what does it do?

The Mercury Precision MerCathode system provides automatic protection against galvanic corrosion. It is a solid-state device that operates off a boat's 12-volt battery and provides protection by impressing a reverse blocking current that stops the destructive flow of galvanic currents. If your power package does not come already equipped with a MerCathode system, Mercury strongly recommends that you install one, particularly if your boat is equipped with a stainless steel propeller or other submerged stainless steel hardware. The MerCathode should be tested annually by an authorized dealer for proper operation.

 

So when is the move?

 

My truck originated in Colorado and left there in 2008, so it got some time there. However, it still differs from MN type of winters.

Anything you do to the undercarriage where you clean off the surface rust and put on some protectant, even if it's cheap stuff is still way ahead of the game. Good on you for being proactive about it. You'll have be able to spot any potential trouble spots. Perhaps have those professionally dealt with.

Being good about hitting the auto or self car wash after a storm, etc. make a big difference on longevity.

 

Way to ruin a thread by bringing up horse face.