Welcome from Colorado: I'm one who likes the longer Airstreams as they are more comfortable for long distance travel in my view. Bigger fridge, bigger wardrobe, bigger bath, more storage, etc. The downside is heaver weight, harder to get into tight spots, more windows to clean, etc.
It all depends on your intended use. If you want just a weekend getaway, the camper will work fine. Better than a tent. If you plan on extended stay living and even working from the trailer, the longer trailer will work better.
A 77
Sovereign will likely need a lot of work and expense to re-commission it. The tires need replaced. Likely the axles will too. Likely there are rotted out holes in the 1/2" plywood floor. Likely the appliances will be problem matic. If you have the time and bucks to get it renovated into a comfortable, reliable Airstream, well then okay.
I spent a winter (October to June) on a 76
Sovereign 31'. I feel I know the trailer pretty well.
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 !