i blasted the bed of my truck when i first started on the project and sprayed it down with picklex20. i then put it on saw horses in the back of my barn and left it for 5 years while i finished the cab and frame. every spring when the barn was cool and the air was warm and humid, water would condense on the metal and drip onto the floor. the picture below is when i started back on the bed, the lower parts were getting surface rust and after 5 years you could see an orange tint to the whole bed. i ended up sand blasting the bed again and then epoxy primer before i did any bodywork. so yes it does keep rust at bay for a couple of years but it has time limits.
if i had to do it over, i would blast and seal it with epoxy. picklex20 is good for keeping bare metal stock from rusting.