I wouldnt over think this,
http://www.lowes.com/pd_6058-78-GJBP00203_0__?productId=3586548 that product works for me, a gallon goes a long ways too, I brush it on, do about 2 sq ft at a time, then just scrape it off into a bucket, I do it on the lift with a kiddie pool under where I am working...
We did a nova in the beginning of the summer, who ever built the car did a great job painting the car, but under coated the entire bottom, I thought it was to hide shoddy metal work, but when we stripped it I found nothing suspicious. We stripped it, power washed it, dried it, Da'd it, wiped it down with lacquer thinner, POR 15'd it, then used por15's primer, and then base coat clear coated the entire bottom of the car. Its a friends car, he did all the hard work, I just supplied the garage, lift, tools, and know how...
So, that is what I would do, that jasco epoxy stripper and a scraper.. good luck, it took us 3 days, but we pulled the tranny, rear end, and gas tank out, and also had to strip and pain them, they under cated teh **** out of that bottom, he said there was receipts for 11 cans of rubberized undercoat with the cars paper work, lol..