What to spray in rocker panels and doors

I just bought a 2005 dodge and I would like to keep it for along time. What do you think are the best steps for rust prevention inside the doors and inside the rocker panels. There is not rust on the outside of these parts. What do you think I should spray inside these areas. Should I just spray oil in there.
Thanks

I would use Wurth body wax. It comes in quart containers but you need a special gun with wands to apply it. It's leaves a nice wax film on the inside of the panels to keep moisture out. Many european car companies use it from the factory. Great stuff. I can try to find out where you can get it if you are interested. I have the specific gun to use for it. If you would like to borrow it I would have no problem with that. I'm in Saline, just ourside AnnArbor. It can be messy to apply though and you need and air source. 3M also makes a similar wax, called Rustfighter I but it's not as thick as the wurth.

I used to buy Tuff-Kotes penetrant out the back door - the amber, liquid product NOT the tarlike top coat.

Now I use Rustfre' (clear) - looks and smells the same as the old Tuff-Kote product.

It will creep out on hot days for awhile but cleans up with kerosene.