As others have alluded to, seeing the rot is just the tip of the iceberg; fixing the possible frame rot underneath is a whole different ball game and you won't know how good or bad it is until you rip out the old subfloor or drop the under tray and banana wrap.
If you're a metal fabricator and carpenter with a garage full of tools and welding equipment at your disposal, a new subfloor and fixing any frame damage is doable in three weeks........if you don't have these facilities or skill sets .......
I think based on your explained lack of knowledge (only just learned how to use a drill) this project will be very daunting.
If I were you I would find the closest Airstream expert to you and approach them to drop by and see the problem. They could then give you tips on how to take out the interior gables and subfloor. Then you do the work until that part is finished. Invite the expert back to guide you through the next part of the project, like dropping the banana wrap, under tray, any frame repair and painting. Then you do that work until that's finished. Then invite the expert to help you lay up and lay out the new subfloor leaving you to finish off screwing it down and re-install your interior.
Be prepared to compensate them for their time and mileage, but trust me a good expert would save you a lot of time, money and heartache. Peter H Airstreamer is just such an expert and lives in Austin Texas. If I were you I would contact him to see if he, or someone he knows that lives closer to you, would help you.
PS 99% of Airstream trailers who's owners are faced with this predicament end up placing their Airstream up for sale with the ad saying, "Gutted Airstream trailer waiting your dream interior; all the hard work is done".
Per Mare, Per Terram and may all your campaigns be successful.
“It’s a recession when your neighbor loses his job; it’s a depression when you lose your own.” "Harry S Truman"