Welcome from high dry Colorado: Moisture is the enemy of Airstreams, and the lush, green southeast has plenty of it. You have a major project on your hands. It will bring all kinds of "fun".
As they say, knowledge is power. You will learn lots about your Excella II here on Airstream Forums. I would suggest you find the "knowledgebase - Airstream trailer forums" near the bottom of the Forums page. Then click on ExcellaII and the 81 model year. Finally, read all you can.
I might add that the Excella 31' is very similar to late 70s trailers. So go down a few years and read more about 80, or 79, or 78.
You will need to assess and repair all the rusted, rotted out areas of your Airstream. Start a list. Don't think about interior layouts or decorating until you get the structure sound. You said you want a functional, dry, safe space. That is going to take some hard work. But it can be done.
I've spent all winter working on a 76 Sovereign
31', kinda a precursor to the Excella which I think came out in 77. Marketing names don't mean much, the Airstream trailers of that vintage are made much alike. Anyway, you might like to look over my project thread describing how we renovated my friend's Sovereign
. It will be finished for the summer shortly. I've got about 1200 hours of work in the thing. I'm retired and need something to do. The link to our project thread is below.
Here is a photo of the Sovereign
up on jack stands as it has been all winter.