It's all done with por15 products.
Start out with their Marine clean,
http://www.por15.com/prodinfo.asp?grp=MC&dept=2 this stuff and a pressure washer works wonders.
then use their stuff called metal ready,
http://www.por15.com/prodinfo.asp?grp=MR&dept=2
then put a big ass fan blowing on the bottom of the car and use a high pressure air nozzle to get any water that might be hiding in seams or anywhere else letting it air dry for a while really isn't going to hrt at all.
Then simply put the car on a lift and spray on the good stuff, POR15
http://www.por15.com/prodinfo.asp?grp=1&dept=1
I'm not gonna lie it's time consumming and costly at the same time and I'm sure it would be a pita w/o a lift and a decent size compressor. But damn after seeign this I will do my next car the same way for sure.