Originally Posted by Lyvettely
What is the underbelly pan?
What is the banana wrap?
Why do you have to remove the banana wrap in order to replace (or slide in) the bathroom floor?
--The belly pan is the sheet of aluminum that encloses the bottom.
--The banana wrap(s) are the curved pieces that go from the bottom rub rail to the belly pan. I'm not certain, but I think of them as being the compound pieces at each corner. The simple curved pieces along the sides are just "skin."
--Why remove? Well, when you remove the rub rail you will see that that the banana skin comes up to meet the shell at the C channel and overlaps the upper skins at that point. Maybe it would be better to say that the shell is attached to the C channel and sits on top of the plywood floor. The banana wraps come up past the floor to attach and overlap the shell. So it's the banana wrap that conceals the floor. If you're going to slide new floor in, the banana wrap has to come down. It's actually not that big a deal. Drill out 20 or so pop rivets that hold the rub rail on and the then the ones that attach the banana wrap to the shell then the few that attach the banana wrap to the belly pan (actually, take the belly pan ones out first) and viola, you are looking at the edge of the floor.
Some members do cut out sections of the floor and replace them without going under the C channel. Nothing wrong with that if you've got a localized weak spot. However, most rot is along the wall and is either so close to it or under it that you can't put in a doubler underneath, so you're forced to take out the floor under the C channel--that may be a small section, not the whole 4' panel.
If you ever plan to tow your Airstream, you should do the floor right while it's accessible. I would think that also goes if it's a full-time apartment. On the other hand, if you're just using it as a once in a while guest room, you might see if laying down a pergo-type floor gives you enough stiffness. This would really be a last-ditch solution, since there's usually rot around the door and you need to have a sound floor in such a high traffic location.
You can get an idea of what it takes to slide the floor out in posts #7 and 8 in this thread
where the C channel bolts are visible. You also need to remove (usually by cutting, due to rust) the "elevator" bolts that hold the floor to the frame (which means the belly pan has to come down).
The good side of this is that you'll discover the rusty frame and in no time you'll have your wire brush out and soon you'll be POR-15'ing the frame and feel really good about it!