If you own a Toyota truck you need to take care of it so it doesn't rust into oblivion. Toyota/DANAs coating is/was completely inadequate. I've had luck using rustoleum clean metal primer/ rusty metal primer and black rustoleum paint.
POR-15 is crap-- peels off in large flakes after time. Not worth the money.
Interestingly, the trucks at a dealership in Colorado now have the frames coated with some sort of hydocarbon-- I swept my finger through it when I was there last. My truck wasn't coated like this when I bought it from the same dealership in 2006.