It depends on what you are looking for. If you want quick, easy, and light, you could just attach a plastic dog kennel to your rack, either permanent, or take it on and off. I'm in a deer hunting lease, that still allows hunting with dogs, and we've been doing this for years. They come in several sizes. The large can haul 2 hound dogs easily. There is an extra large too. Other than that, have a welder custom build you one out of aluminum, or I even think there are companies selling them already built.
This guy seems to be a lot more serious than we are, but I think one box the right size would work. lol