I had the same thing with my 46 COE. I clean everything as good as I could,blast or wire wheel and then soaked it down with Jasco prep and primer. It has the consistensy of water so it gos any where water went. It turns rust so hard I had to use a chisel to break a hardend puddle of off my floor! I used a deck sprayer. It's very toxic so be carefull,read the label. Best to let it dry for days.I got it at Lowes in a quart bottle.I soaked the body ,frame everything with the stuff and my truck was very rusty!! Hope this helps

1946 C.O.E. with a Holmes Traffic King Wrecker