One of my sons owns a house in another state and spends part of his time there. Since he takes his family, he often is carrying quite a bit of stuff with him on these trips. While he has a pickup due to the size of his family, it is not always convenient to take it and he often takes his SUV. He solved the problem of how to carry extra supplies by building his own cargo hitch carrier.
Now most cargo hitch carriers are simply a platform for you to tie items too. This always presents a loading problem. He solved this by making his own in the form of a large rectangular box. He used aluminum diamond plate for the sides to keep the weight down while providing strength and a long life. His was build from scratch and is quite strong. The bottom frame is steel angle, iron the rest aluminum. He estimates that it will carry a 1000 pounds plus without any problem.
Remember that a big factor in how much weight your box will carry depends on the rating of the tongue weight of your hitch. The tongue weight capacity is the maximum vertical weight that the hitch can support.
To prevent problems with the police he has a bracket for his license plate and lights on the back. The lights are LED lights that include brake and stop lights. The wiring is all protected inside the box with aluminum angle iron.
At times in the past, he has used a small trailer to carry items to his house. The advantage that the box has over the trailer is that you are not limited to driving 55 miles an hour since you are not pulling a trailer. At least in his SUV, he has not had any problems with handling and it drives normally.
He has also added a cargo carrier on the roof and between them he can carry a surprising large amount of supplies. He added some tie downs to his box and covers it with a tarp to protect it from the weather when he is traveling. This box has already traveled several thousand miles while carrying a full load without any problems.
For those of you who do not have access to pickups or trailers, building a cargo hitch carrier may be a way for you to increase the carrying capacity of your vehicle while bugging out.