Hello from Colorado: Welcome to Air Forums. I presume that Caravelle sat in the Oregon woods for 10 years. It is wet in Oregon, right? Moisture is one enemy of Airstreams.
So you have to presume there is moisture damage, varmint infestations, mold and mildew everywhere. It's will be a big project to get this trailer back on the road. Maybe even taking the body off.
Assessment of a project trailer is pretty easy. It needs everything. Your assessment might focus on the possibility of towing it home. Tires, bearings, brakes, frame, coupler and exterior lights need to be working. Next is the body. Big demerits if a tree fell on it, or hail damage, or missing and/or broken windows, and the door won't shut tight. If it has a good body, well, that is the most valuable part. Airstream aluminum bodies last a very long time.
If I recall correctly, the Caravelle line was built as a lightweight trailer so you could tow it with the light weight cars of the 70s.
So if the body is good, and if you can tow it home, it might be worth $4000 or so max. And then budget maybe $12000 and 1000 hours of labor to get it fully functional with upgraded stuff.
Just my friendly opinion.
WBCCI #8607 VAC Region 11
KnowledgeBase trailer renovation threads: 69 Globetrotter, 76 Sovereign, 75 Overlander, 66 Trade Wind Such fun !