At this point, the shims were replaced in their original positions and the body was lowered back on to the frame.
To lower the body, we place the porta-power between the body and the frame rail near the traction bar attachment point with a steel plate between the body and the porta-power, raised the body slightly to remove the temporary shims and lowered it.
All body attachment bolts were replaced and torqued.
The main box was riveted to the floor by drilling through the original rivet holes.
Body seam sealer was used to fill the void between the fiberglass rocker and the bottom of the rocker rail. Also to cover the welded seams and to fill any other voids.
Paul coated the torque box with epoxy primer...
...and we covered that with rubberized undercoating.
There are several options to rustproof the interior of the torque box. One option is to do nothing. The original boxes lasted almost 50 years (maybe more) with no treatment. These cars will most likely not get the same exposure to the elements that they originally received.
Another option is to purchase stainless steel torque boxes from Classic for a slight premium.
You could also use a weld through primer on the inside of the box before you installed it.
What I chose to do is to drill several holes in the floor of the car with a hole saw in the center of the torque box and spray a wax based rust preventative compound (available at professional body shop supply stores) into the holes, then to plug the holes with plastic plugs. You could also add some closed cell foam if you wish.