Gatlin’s BBQ, located just a few miles from downtown Houston, might have the best motto we’ve ever run into on our barbecue tours. “Welcome to Gatlin’s,” the sign said. “Where love is the secret ingredient.” And if you want to experience the reality of life in a no-zoning, anything-goes big city, this is the place. Next door is a garden expo that looks like a nursery. Directly across the street are an engine repair business, a house where people live and an automotive sales building. Welcome to Houston. Gatlin’s gets rave reviews from some, but the Posse was underwhelmed. “If…