After I posted this thread yesterday, I got to thinking about what problem I'm really trying to solve. I believe it to be the size of the ground path back to the MH. Grounding to the Vue's chassis, even though I'm sure that it is good and solid, doesn't help with that. I started to wonder what might happen if I tried to ground on the baseplate, too. That might give me a ground path back via the tow bar.
We are in the middle of an ice storm and it will last a couple of days. Afterwards, I might slip out and measure the resistance from the baseplate back to the MH with only the tow bar connected, not the light wire. If that measures out with low resistance, I can try splitting the toad harness ground wire and making a connection to the the baseplate.
2000 Georgie Boy Landau 36' DP
2005 Saturn Vue toad