Welcome from Colorado: Glad you are interested in renovating an old Airstream. The trailer in the photo is a project indeed. The price reflects the "as is" condition.
This old 68
Sovereign is the "International" trim level meaning it was the top of the line trailer. It is the last year of the "old" body style. The new body started in 69. Some say the older body style is more "vintage" looking and thus more valuable. The cabinetry in this trailer was very nice veneers compared to the base model. Some folks say the 68 trailers will be classics. That said, the longer trailers are not as popular as the cute little ones. It may be more difficult to get your investment back out of a longer trailer judging by the classifieds. The mid sixties trailers had unique windows and some other hard to find parts. I did extensive work on a 66 Trade Wind base model.
The 70 Ambassador is nice too. The new body style had rear body to frame sealing problems causing rotted rear subfloors and rear end separation; which can lead to damaged frames. The vista view windows were prone to leaks causing more floor damage. I now have a 75 Overlander that did not come with vista view windows. That was a plus for me. But it did have rotted rear subfloor and rear end separation. I've repaired all that. I was looking for a project trailer.
If the windows in the 68 are there, and most of the interior is there (used as patterns for new pieces as required) and maybe you are prepared for a "body off" frame renovation, I think the 68 would be worth more when done.
David
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WBCCI #8607 VAC Region 11
KnowledgeBase trailer renovation threads: 69 Globetrotter, 76 Sovereign, 75 Overlander, 66 Trade Wind Such fun !