Heat the oven to 250°F. Arrange 2 racks to divide the oven into thirds and heat the oven to 250°F. Line 2 rimmed baking sheets with parchment paper.

Make the seasoning mixture. Place 8 tablespoons unsalted butter in a medium, microwave-safe bowl. Microwave in 10-second intervals, stirring between each, until fully melted, 50 to 60 seconds total. (Alternatively, melt in a small saucepan on the stovetop over low heat.) Add 2 tablespoons Worcestershire sauce, 2 teaspoons seasoned salt, 1 1/2 teaspoons garlic powder, and 1 teaspoon onion powder, and whisk well to combine.

Combine the Chex mix. Add 4 1/2 cups Rice Chex, 4 1/2 cups Wheat Chex, 3 cups pretzels, and 1 cup peanuts, and lightly toss to combine.

Toss with butter. Pour half of the butter mixture over the Chex mixture and gently toss to coat. Pour in the remaining butter mixture and gently toss again so all the pieces are coated in butter.

Bake until lightly brown and crispy. Transfer the mixture onto the prepared baking sheets and spread into an even layer. Bake, stirring every 15 minutes, until lightly browned and crisp, 45 to 50 minutes total. Let cool for 10 minutes on the baking sheets before serving.