Well, I went & clicked on the link you provided. Now my curiosity is really up.
What was on the circuit that initially energized the frame of the mobile home?
I've had a similar problem in the past & what you may be looking for a high impedance ground fault in an appliance. This fault would impress line voltage on the frame, but the resistance of the fault itself may be so high as to limit current flow to such a low value that it is difficult to measure. Also, the fault could be on a busted or damaged neutral in the appliance.
Whatever the problem was that put the voltage on the frame probably still exists.
You might try making your own current transformer for your clamp on & putting it around the new bond wire you installed. I'd bet that it is carrying a small current in the Ma range. Try you lowest scale on the clamp on, with one piece of insulated wire, wrap 10 turns of wire around one jaw, wrap one turn around the bond wire you installed, then connect the two ends together with a wirenut. Divide any reading you get by 10.
Looking forward to the next thrilling adventure in the continuing saga of "minimum standard wiring."
