Hi Scott... I agree with all of the above advice. One point tho'
Don't use the expanding foam! I used this years ago in a VW bug I restored. BAD IDEA! , It retains moisture in the box sections,not good! If anything use a good quality rustproofer. I'm using Waxoyl (after all the paintwork is done!) As the name suggests it's a wax based product and 'creeps into seams and voids etc.
Jock. thumbs_up

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.