Shell off is just that, getting the shell off of the frame. It requires getting the inner skins off in order to be able to access the bolts. All of the stuff inside needs to be taken out in order to fully access the inner skins. Only the lower half of the skins need to be removed (if possible, it depends upon the overlap)
Carefully brace the shell inside so that it does not warp when removed because of the spring forces the bent metals put on it. Otherwise It may cause issues trying to put it back down later. The bolts are cut off with a sharp chisel, putty knife or in the case of a well rotted floor a reciprocating saw. One of those new vibratory saws might work great with a blade rated for cutting metal.
Once the shell is up, pull the frame out from underneath and assess the frames needs. Once those needs are met, put a new floor on using "Elevator bolts" just like the ones you cut off. I recommend several alterations to eliminate the need to replace the floor again. Use Marine grade plywood,
Costs more but worth every penny. No voids, waterproof glue, and better wood to begin with. If you can work with fiberglass, fiberglass the outer foot over the edge to not give water any access to the end grain. This will also force any water that does get in not to be able to hide. One layer of mat is sufficient and can easily be sanded flat when cured.
Carefully align back the body by pre-drilling the holes that are at fixed points and align to previous points on the shell... be careful, the outer parts of the frame can easily flex out of position. If both the frame and shell flex out of their previous positions it can cause issues when things go back together inside.
Reinstall inner shells and then interior components and check to make sure things work as they should as they are reconnected.
The Full Monty takes this to a whole new level since you would replace all of the wiring and plumbing. Add tanks where there pretty much were none.
Update/upgrade systems and appliances, etc. until you run out of time, money or both.
To make it short.. the Full Monty is a Part time project that will take a loooooong time to complete. The Shell Off will take much less time and will likely save your marriage and sanity...