These guys actually go a little over board with these bodies .Shelby and other racers raced these cars for years without problems ,and they were not gentle with them .
Rust proofing would be the best thing that you could do .Prime inside and out ,there were a lot of places these old cars never even saw primmer, like up inside the quarters , and look how long they lasted any way .
Seal them well with seam sealer ,if water cant get in it doesn't rust .Cowl areas are the worst ,it is hard to prime or even paint inside .An old garden sprayer with a wand and spray up in side the cowl ,rockers and any other hard to primmer spot will stop a lot .
Seal the windows well ,the biggest problem with rotted floors is leaky windows .
New door seals ,trunk seals and any other rubber seals will help stop a lot of rusting problems.
Keep all the drainage holes clear ,in some cases enlarge the drainage holes such as the bottoms of the doors .
The doors them selves need to be primed well inside .
Most of these cars will never see the use a regular driver will see ever again .My last 65 fast back saw less than 2,000 miles a year . I had it for 10 years before i finally sold it .