I say to leave them, like said, it is the dirt and junk that absorbs moisture that causes the rust, IMO. I like the idea of rinsing the cab corners out with the garden hose every so often in the summer so there is not dirt accumulation, usually in the summer so it can dry back out.

 

The truck is a 56 with the gas tank moved under the bed. I am thinking I will leave it sealed and por-15 the inside.

 

That reminds me of something about my great uncle. He took very good care of his trucks to try and prevent them from rusting out. He would wash them in his driveway after every drive, especially if there was salt on the roads. He eventually made a little wand to attach to the end of hose that was bent upwards so he could poke it into the drain holes in the door and such without bending over. Very particular man when it comes to keeping his trucks clean.

 

I like your great uncle. I put tee in the hot water line for the washing machine and ran a hose off it for those days I had to drive on salted roads. Think of Doc's sponge analogy and now add salt to it. It just sits there all wet and rusts out the truck from the inside. Drain holes work when the vehicle is clean and new.