Here there is a little more for that Mod ... I was looking info cause it seems a good addition to long trips for my daughter ... Im sure someone could take the idea and DIY . Agree $325 is at least $125 over the price I would considerate to pay if needed
http://fukushin-ind.com/hummer_rk-tori-eng.html
http://fukushin-ind.com/files/Hummer_H2_manual_eng.pdf