I think that grounding the bus chassis through the AC power panel is a reasonable thing to do. If a house was built from steel studs then any metal electrical boxes that were attached to those studs and were grounded to the main panel would also ground the entire steel stud structure. From a safety standpoint, this would actually improve the grounding protection. If I was only installing AC power in my bus there would be no question - I would ground the chassis to the bus panel, and through the extension cord, back to the shore power panel. This is a proven, safe system.
My only concern here was that the AC and DC systems might not play well together, but since there are many who have their AC panels grounded to the chassis it appears that this isn't a problem.
Looks like I just joined the "ground AC panels to the chassis" camp.
My apologies to the OP for helping to hijack this thread. We promise to play nicely in the future.