This is what I was doing the last few days. Later on I'll post pictures of what it looks like now, with the new framing, insulation, and flooring. Basically the entire rear floor, under the bed/couch under the window, had been destroyed by a combination of water damage and termites or carpenter ants. There was no framing left in the rear 4 feet of flooring, it was just dust at this point. We ended up pulling out an entire wall's structural members and floor studs: there was a lot of day light coming through. This is the most structurally-intense renovation/repair I have ever had to do in a trailer, but it was similar in nature to the repairs I had done to fix water damage in other trailers, so progress has been going very quickly!
I'll walk you through peeling back the layers of rot. Don't let this discourage you if you're considering repairing your own vintage trailer. If I can do it, anyone can. Oh, and a big thank you to my friend Matt for helping me out in these hectic weeks before Tiny House Summer Camp, and all the other weeks he's helped as well.