I used one quart and it did my whole frame. No need to take the tub off, brush it on and around any body mounts or other items in the way. Tape off anything you don't want it to get on (body mount bushings, e brake cable, etc).
Two recommendations
1. Wear long pants, long sleeves, hat, gloves, and preferable a respirator if you have one. The fumes are pretty strong and if it gets on your skin you will have fun trying to get it off.
2. I did mine when it was in a grass back yard so I didn't worry about drips, but if you do it in say your parents garage make sure you throw a tarp or cardboard or something down.
It is not UV resistant so the spots that see direct sunlight will need to be top coated with spray paint or something else. Also is goes on thick but I found it has a tendency to peel and flake off after time. That may be related to the the UV on mine though bc I didn't put anything over top of it. It's a messy job but once you get under there and get going it will go quick. Plan on using the whole container once you open it.