I recently installed one myself that I purchased through Absolute Steel (absoluterv.com). I was very impressed with them - they delivered exactly as promised and the final product is very sturdy and solid. I was missing a few screws in the kit and one call had them sent out via express mail to me. I highly recommend this company, and especially Jennifer Morton who was the sales rep I worked with.
Be very careful who you deal with - check BBB listings for companies you consider. I first ordered a carport from Coast-to Coast carports to be installed by them on my property. After a series of delays and excuses, I cancelled my order and had to argue with them to get my entire deposit back. With a little research, I discovered that all three of the companies listed on carports.com (TNT, Coast to Coast, and American Steel) are listed with the BBB under the same owner name, and they have TERRIBLE ratings. I wish I'd discovered that before I placed my order with them.
Again, I was VERY HAPPY with Absolute Steel. The only issue was that I had to build the carport myself from their kit. The included instructions made this easy enough to do - simply assemble the ribs flat on the ground, then have some friends help lift them into place and attach the roofing sheets. I used the RV itself as a scaffold - working from the roof of the RV to place and secure the uppermost panels. If you are unable to build it yourself, there are plenty of out-of-work construction guys around who'd probably be happy to have a day or two of paid labor. It doesn't take any special training or skills to do the job.