I guess it all depends on how much work you want to do. Some of the forum members have done it with the shell on and replaced it in sections, and others have taken the entire shell off to replace it.
to get at the bolts holding the shell down, you will have to remove the lower interior skins and you will see them.
If you go into the forums and look under repairing and replacing floor and or frame, you will find out just how much fun it can be.
I live pretty close. If you have any questions, you can IM me.