Thanks for the reply.
I will not have access to the MH for a few days, but will verify output of converter at that time. The buss bar is steel and it is rusted. Had to remove the batteries to get access to it. It is rusted and was unable to remove the bolts which secured the battery leads. I will use a penetrating oil next time to see if I can remove them.
I was surprised that using a jumper cable to connect the battery ground to the frame did not fix the problem. Perhaps it was not making a good enough connection. Or maybe there are other issues.
Will use a Dremel tool to grind the rust off of the buss bar if I can get the bolts out.
Didn't know if I was missing something. Seems like everything points to a ground problem, but maybe I am not seeing the forest because of the trees.