how hard is it to....

notch the frame on an suv? do you have to pull the entire body off, or is it possible to skip that step by cutting the floor with the body on? yes, i have a lot of questions. i'm sorry. but i'm really interested in learning more. i know the basics, i've been into customizing my entire life. but i haven't learned much about minitrucks, or the bagging process i should say. so any help is greatly appreciated.