That seems to be, according to Martin, one of the primary motivators for the 'hybrid' Silverado- bring yer own genny and free up bed space to haul revenue-generating stuff instead of support equipment.

Save a little fuel while driving, from idle-stop, and built-in power generation at the site. And don't forget- the truck engine has much better emisisons controls than a standalone generator (which has almost none). It also uses less fuel since the ICE only starts up when a substantial load is drawn, unlike a standalone.

Once everyone is comfortable with higher-voltage systems on vehicles, idle-stop will become very widespread among non-hybrid vehicles of all classes.