Not sure what coroseal is, but I remember an paint an body guy (before environmental protection) that save his old oil. Every spring he would coat the inside of the frames of his vehicles with the stuff and let them set for a day. His cars never rusted.
As for the other parts of your plan. If your are pulling the frame, have a pro sand blast it. Probably cheaper than you think.
There are a couple of good products. POR is one. I've had great results and nightmare results. Be sure you follow their instructions to the letter.