JD BOB,

Go to your local NAPA store and buy a bottle of Triple Etch. It is a zince phosphate etching wash.

I sanded portions of my flatbed down 2 years ago and brushed on some triple etch. It has sat outside since then without a hint of rust.
It's a cheap solution. When you are ready to paint, wipe it down with mineral spirits.

BigMac
Thanks Dan