Go to the Article: Tips & Tricks: Use a Cooler to Keep Barbecue Warm
Or, dare I say it, use the Anova Precision Oven (combi oven). You can hold it forever (which can actually improve the final result).
My new GE Profile Smart Indoor Smoker actually has this great function where after cooking is done it can hold food at 140-170°F indefinitely (programable).
