The AF 990 is a 10' camper, so you should be able to use an extension around 24" - My 9' AF811 required a 28" extension on my short bed Ford.

With the weight you want to tow, you will not need a SuperHitch unless you have later plans for something heavier. If you can stay with 2' extension, I think the OEM hitch will handle the leverage of load. I would still use side chains on the extension to limit lateral forces on the receiver.
If you have use a longer extension, I would not put my trust in the OEM receiver. You could replace it with 2.5" Titan and 2.5" extension, but I would replace it a SuperHitch at this point and not worry about having enough capacity in the future and having to do it again.