I discovered my rocker panels were rusted soft 2 days ago and put my finger right thru the driver's side. A co-worker of mine is a hobbist welder and knows of a site where you can get replacement rocker panels for about $150 each side shipped. I went there and it's true. He knows where the weld tacks are on the truck so I'm going to replace my rockers with new ones and prime/treat the inside before we put them on. The site has every body part you could want for the truck and the prices are pretty reasonable.
http://www.lmctruck.com
To answer the closed reply regarding cause - this truck spent it's first6 years lowering boats into the great salt lakes, so it was exposed to a LOT of salt. Something I should have considered before buying it.