Well... I have to admit I didn't do -anything- of this sort. I actually calculated Bertha in such a way that I hoped to get 200Tkm out of her and then... well dump her in my garden. At one time I did not even bother to change oil for more then 70Tkm :P
However on close inspection from top to floor (I wanted to be sure about the cars body before I spend $$$ on the timing chain) I hardly found any corrosion. Only the axles had surface corrosion and I took care of that as good as possible (rear axles are quite accessible, front not so much).
Regarding the body I only found a sad spot at the back wheelhouse (drinkers side). Something wrong with the sealing there and I found actually a small hole. Pity... I think I've dealt with it properly for now but I still consider welding it tough.
After that I used lots of fluid-film for all cavities and spend a generous amount of bitumen anti-rust in the wheelhouses and her floor. I think Bertha really deserves it now and she will get much more attention in future
After all I am quite impressed how little corrosion there was. Especially since she is my -daily driver. Every day, every season, summer, winter, snow and (lots of) salt without even bothering with any maintenance on the body for more then seven years.