the gmt800's really have never needed them which is why there are limited options
the gmt900's on the other hand will throw mud all the way up to the middle of the windows, that's just how the moron engineer at gm decided to do it.
i would look for some short ones maybe, there may be some logo ones out there that might be your best option, the longer they are the less likely they will fit right.
and they all mount to plastic pretty much if you use the little metal tab clips and screws you should be fine