The entire interior (cabinetry, furnishings, and interior skins) are all held in place with pop rivets and screws. The rivets can all be drilled out with nothing more complicated than a drill and a bit. A spring loaded center punch sometimes helps as well. If you look on Vintage Trailer Supply's website, they sell bits that cover all of the rivet sizes you will need to drill out.
Split Point Drill Bits
To reinstall the interior skins, you will need lots of 1/8" pop rivets and a rivet gun. I have used the cheap pneumatic rivet gun available at Harbor Freight, and it has served me fine. There are too many rivets to bother trying to do them all with a hand operated rivet set, but if you want to work your forearms, any old $5 hardware store tool will do the job.
If you want to replace your subfloor, you will have to lift the shell, as the floor is sandwiched between the shell and frame. This will require you to drill out the bucked rivets that hold the shell to the C-channels. Here is where a centering device for drilling the rivets may come in handy. I think I bought mine from "The Yard", which sells aircraft tools, but I have since found that a punch and bare bit work pretty well also. A sharp putty knife is also handy when separating the shell fro the chassis.
If you are going to lift the shell, I would build some wooden gantries and use a couple of cheap chain hoists to do the lifting. I'll post a link to a thread with gantry plans in a moment. I used the 1 ton chain hoists from Harbor freight. Did the job just fine.
When you put the Shell back on the frame, you will need to buck-rivet the rivets back in place. Vintage Trailer Supply also sells a complete buck riveting kit:
Airstream Buck Riveting Kit
Now, the question I would have is: If you don't intend to use the trailer as a trailer, and only as a stationary spare bedroom, why do you want to go through the grief of floor replacement and insulation replacement??? If your floor is soft, you could just slap a layer of plywood on top of the original subfloor, and call it good. No, it isn't the RIGHT way to fix a floor, but it will keep your guests from falling through the original. Likewise with the insulation--it is a huge undertaking, and unless you can smell rotting rodent carcasses, you will likely not improve the insulating capability dramatically by sticking in something new (even using the relatively costly space-age stuff available today). You have less than 1.5" of wall thickness to work with--these trailers just weren't designed for extremes of temperature.