Hey yall, the more I read over this thread the more I feel I want to add my opinion.
I plan to groud the "house dc" to the frame as I plan to charge the td battery with the vehicle charging system. Even though I did not depend on the frame as a conductor when wireing the tailights etc. the ground wires which I ran to each light is also grounded to the frame. I feel the two DC systems need the same negative reference in this case, which will be chasis ground.
Grounding the ac to the chasis and aluminum siding is probably a good safety measure could prevent a bit of a shock in some instances. Checking the outlet before you plug in the trailer is also a good idea, at least you will know it was right before any grimlins came along. The little plug in outlet testers with the 3 lights is all that you need for that. If the ac ground were to become energized with 120 vac you would have an energized chasis, true. But there wouuld be no path for the ac to follow through your DC system. Electricity travels from the source, through the load, back to the source (and takes the path of least resistance to get there). There is no path back to the source through the DC system so it would not be harmed. If you feel the grimlins are out to get you, drop your safety chains on the ground when you unhook the trailer (that should provide a lower resistance back to the source than your body.
My plans are to ground both the AC and DC to the chasis, but not to bond neutral and ground in the trailer (that is done at the park power supply breaker box). If the ground wire is hot at the breaker box you will know as there will be much smoke and glowing copper before you plug in.....

and your little tester will have informed you of the problem if not.
I do carry a very short (about 1 ft) extension cord with the hot and neutral reversed to make it easy to connect properly to imporperly wired campsites.
Do not take this as advise, I am not an engineer, I do have many years of experience working with high voltage transmission and distribution protection and controls so I feel confident that my plan will work for me.
As a side note, my 5th wheel trailer has both dc and ac grounded to the chasis, neutral is not bonded to ground. That's the way the factory wired it and it has served me well.
