I discovered a pretty well documented unibody bed resto (the restored truck looks great) here...

1961 Ford Uni-Body - Bodywork

it shows the basic construction of the bed.

It looks like the ford engineers planned the bed to drain through the openings in the front end of the corrugated bed and into the torque box. Since there doesn't seem to be any way to rust-proof these corrugations, my plan is to by-pass them , and am thinking of using seam sealer to seal the front edge of the bed at the cab. That way at least I can slow the rust process by preventing/reducing the moisture running in the corrugations.

I will protect the inside of the torque box with eastwood's inside frame sealer. I will create another drain path, but will still end up draining into the torque box since whatever drain will need to be at the front end of the bed.

Any other suggestions?