Well Guys, I will have to dissagree with all of those that seem to think that the bodies NEED wood in the sides, in over 30 to 40 years, I have NEVER wooded inside any body, except for the floors and inside the firewall, all 5/8" or better... When doing the inside of the firewall, stand the body up on the firewall, grind any seams or junk that is present, so that it is nice and flat and clean...Lay in a thick layer of (WET) mat, place the plywood firewall backing on the wet mat, apply weights to that plywood, buckets of sand, old metal whatever you can find for weight... let dry over night, then the next day apply another layer of mat all around the edges of that plywood to seal it up real good to the body, now it is one piece, strong as all get out, great to mount your steering column to with only 3 or 4 bolts needed, no other brace of any kind needed, just check out any of my old bodies from over the years, and remember that CCR was my company, they still do it the same way...
Someone mentioned seams in/on the outside of the body, well they are there because the molds bolt together there, and that means nothing as to the strength of the body, just need to be sanded off and primed and any filler to any pin holes is now done...
Many years of many people, hundreds of people climbing in and out of my T Bucket has never hurt my body, had them scratch the paint a time or two, an easy fix.... press on any new car door and tell me just how SOLID it feels, I will take a bit of flex any day, all it is holding is paint... MY VIEW, You do as You like.