[mandolindave]

It's obvious that you are on the ball, have good taste, and like cool stuff.
So for now you are researching the feasability of gutting an Airstream and
transforming it into a healthy green living pod.
I am sorry but I think that I gave advice, only with insight looking through my own glasses while sitting on my empty wallet. Now that I know why you want a trailer specifically for gutting, it all makes sense. But I would get an estimate from a company that restores Airstreams?

Trailer insulation can easily get moldy. Plan on gutting the interior walls to get at the insulation. Someone here on the forum redid his interior with aluminum panels. It looked real nice. Try a search on ozone generators, for eliminating mold. Also if you don't run your fridge nonstop, or leave the door open, it will develop mold in a heart beat.

Another Airstreamer replaced his ABS plastic tub, and had a stainless steel tub made. (You can clean stainless with olive oil ).

You had a question about vents. Fantastic Fans, are very popular option to have installed in the ceiling vents. They work well and are efficient. But they suck heat out as they are exhausting the gallon of water that each person exhales or sweats out each night. As stated, RVs aren't good in winter climates. Water coming in and waste going out is prone to freezing.

To Natasha, Non Formaldehyde enzyme based waste water treatments
like Ridex powder, are available at many grocery stores, and home centers. A little more expensive ( not neccesarily better or healthier ), green liquid enzyme types ( like RV-Trine) can be found at RV stores.
Those are the two that I use.