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I would go with 3-4 days max. Your limitation is the gray water. That is a really small tank. No showers, just sponge baths. We had a Casita trailer with very similar specs, and that was about what we could get.
We carry 2 extra 6 gal water tanks. If you use the outside shower. Then you don't haft to worry about the gray tank. Stock up on paper plates and plastic Utensils. I think a weekend is more realistic