I have not had much time for Studes this year but I am almost complete with 
building the boxes on my 64 convertable. I am using 1/8 inch 2 inch angle 
iron. I did not strengthen the body when I removed the hogs. I knew one side 
of the old boxes had some rot but when I removed the undercoating I found 
the inside side of both of them was gone also. I do not understand this as 
after I removed them i had shiney floor board metal underneath them. I had 
to adjust the drivers door a little but did not have to adjust the passenger 
door. The drivers side of this car is actually the worst side as far as rust 
goes, which is really strange. These floor boards are really solid with only 
a couple small patches( installed before this effort) so I figured removing 
the rotted out hogs would not hurt as they were not really doing that much 
anyway.  When I removed the original boxes I think I could have filled a 
trash can with all the hunks of rust that came out.   These things looked 
much better on the outside than they were on the inside.

I built the boxes by using the angle iron to form a u channel on the inside 
and outside of each box. I used this method as it allowed me to manever 
around the frame supports.  I could not have gotten a u channel in there 
with the length I used.   The outer rails are close to 6 foot in length 
which gave me the strength I wanted as they run from the front floor boards 
to just in front of the rear wheel well.  This is my first convertable and 
it seems that the area under the rear window was not supported as well as it 
could have been originally as that water running down into there from the 
rear window had a poor design for removal or draining..

I placed a galv plate across the bottom of the two u channels ( two pieces 
of angle used to make a u) I really think the 8 pieces of angle I used are 
better than the original hogs but they do not look as nice I guess. I 
attached the bottom plates with screws and caulking so i can get in there 
again if i ever need to. I ran 1/4 flat steel from each of the frame mounts 
across the two u channels.

This method seemed to really work for me, the 1/4 flat steel supports the 
outer u channel and still allows me screw the plate on the bottom. The galv 
I used was pretty heavy and I put two ridges in it to add strength.

I do think that the door I had to adjust was due to the fact that I 
"repaired" a saggy floor and someone previous had adjusted that door to 
allow for the sagging floor.