I use math and calculus to determine the bend locations like I used to when I was fitting and welding pipe in my chemical plant days. Each bend has a bend radius and a gain that you take in effect for each bend. PVC sounds like a hot rod magazine tip or something like that. I would avoid advice from someone that uses PCV to lay out a chassis and calls them self's a chassis builder. I might suggest that you try using a piece of wire or something like card board to lay out bend radiuses. Wire is re usable. The bender only bends one radius, not what ever you can bend wire or pvc to. Once you wrap your mind around the concept I am confident that you will figure it out.
Often the benders come with some starting instructions that you can start off with. As for the bender, the type will limit how many degrees you can bend any one bend. Some will do 180 deg and most don't. The bend quality must be wrinkle free and without necking. Mandral bending is not required but a good bender is. The key to a good bend is lube and clean, clean, clean.
Now the body. Cut her loose and mock up a brace that you can use to hold it safely in the corner for measurement purposes and trial fits to your cage.
This is the only way any car can be perfectly strait is by putting it that way. When I mount the body I try to be sure that every thing chimes ( Is perfect as possible) to every piece of the frame centerline.
Remove the doors and re mount them later when you are mounting the body for the final fit. You can make the car better than the factory ever could have. Stay with it and go one direction and you will get there every time guarantied.
Bruce