For those of you looking at adding shore power to your truck, or trying to find a better way, I found this in my "travels". It looks like a pretty slick little unit and a much better solution than the simple relays I've seen. They're a little under $200 everyplace I've seen them.
Rapid (16-26 msec) Mobile 3 Way Automatic Transfer Switch
Rapid (16-26 msec) Mobile 3 Way Automatic Transfer Switch