Preheat the oven to 250 degrees F.
Toss the tomatoes in bowl with the olive oil. Arrange the tomatoes, cut side up, in a single layer on a parchment or foil-lined baking sheet. Sprinkle with the salt and the crab boil seasoning or celery salt. Bake until slightly shriveled but still plump, 5 to 6 hours.
If not using immediately, refrigerate the dried tomatoes in a sealed container for up to 4 days.
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