Here are some pictures of various roof racks, with a bit of emphasis on the one I use.
1. Modular vs One Piece
In my case, I chose to go with a one=piece roof rack. My reasoning was that it was more durable and less likely to come apart on the rough trails we normally see. Besides modular vs one-piece, there was one other option - steel or aluminum. Steel was the ultimate choice, and the reasoning was, again, durability and strength.
On a recent trip to the wilds of Southern Utah, we often needed to navigate trails that were just wide enough for ATVs. In one instance, being the widest vehicle in the group, I usually cleared a path for everyone else. As the trail narrowed, due to tree branches and brush, I needed to pass through this one particularly narrow section of the trail. Going to the right was not an option nor was going to the left. So, on I went, and in the process, a rather large tree branch managed to get tangled in the roof rack. As I continued forward there was a loud crack and I knew that one of two things had broken. Fortunately, it was the branch. The rack was not affected at all.
The tree branch that broke and fell on the roof

- Hummer vs Tree branch-2.jpg (4.41 MiB) Viewed 806 times
One of the tree branches

- Hummer vs Tree branch-1.jpg (154.33 KiB) Viewed 806 times
What a one-piece rack looks like. This rack is a powder coated, fully welded steel unit (not modular) that uses the entire space on the roof of the Hummer. Fortunately, the H2 came from the factory with two steel roof rack rails, which this rack utilizes. As seen in the picture below, the rack is held in place, in the rails, by 12 stainless bolts.

- Modular vs one piece.jpg (950.13 KiB) Viewed 806 times
2. Accessories For A Roof Rack
The location of the roof rack, being the tallest portion of the vehicle, makes it a prefect location for antennas. When done properly, the antennas will not interfere with the storage space. Here are suggestions for both an HF antenna and a 2M/440 antenna.
2M/440

- Roof Rack 2M & 440.jpg (277.35 KiB) Viewed 801 times
HF

- HF Antenna Mount.jpg (1.85 MiB) Viewed 801 times
Roof racks are perfect location for awnings and wind turbines.

- DTK Wind Turbine.JPG (102.17 KiB) Viewed 801 times
3. A small sampling of gear that can be stored on a roof rack

- Roof Rack-1.jpg (210.17 KiB) Viewed 801 times

- Rack with firewood,gas.JPG (146.92 KiB) Viewed 801 times
The natural concern that most will have, is how dirty my clothes or tent will get on the top. Given how bulky these items are and how much room they will occupy inside the 4WD, it is fortunate that there are effective solutions. The first is a cover for the rack.

- H2 Roof Rack Carrier w cover.JPG (126.01 KiB) Viewed 801 times
The second is a dry bag.
Watershed Colorado makes a large variety of dry bags, all made in the USA. These bags offer protection from dirt that even the dustiest road cannot penetrate. While you don't often see a clothes duffel riding on a roof rack, a good dry bag can keep the contents completely free of road dust and water.
The Watershed website (drybags.com) sells a full line of dry bags. These bags are water tight and tested to 300 feet, extremely rugged, come with a purge/inflate valve to accommodate changes in elevation, and a lifetime warranty to the original purchaser. They even note that the bags can be stored on top of a vehicle so as to make more room inside. If you are looking for a way to keep road dirt and dust out of your bags, this is the way to go. And, the recommended storage for river rafting. See:
https://www.drybags.com/product/colorado/.

- Dry bag.jpg (21.92 KiB) Viewed 801 times
4. Our Members Roof Racks

- PET.jpg (2.08 MiB) Viewed 801 times

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- DYO.jpg (373.27 KiB) Viewed 801 times

- DGL.jpeg (156.39 KiB) Viewed 801 times

- BCA.jpg (134.72 KiB) Viewed 801 times

- JVE.jpg (180.52 KiB) Viewed 801 times