I found 2 positive cables that are in contact with one of the rear shocks. It is hard to tell, but I'm pretty sure that there is some rubbing on the insulation of the wires. At any rate, I need to re-route the positive cables on the inside of the shocks so they cannot come into contact with the shocks. The positive cables echo the configuration of the negative - they go from the battery to a junction box under the van where they are connected to 2 other wires, one of which goes to the inverter.
It is possible that the wires carrying 12 volts could be shorting on the shocks intermittently through the thinned insulation. The behavior is not consistent enough for a full on short where a positive wire is always shorted but there is some significant heating of wires. We could be talking about a fire eventually if I don't find the source of the problem.
I was talking with my brother and looking at the documentation for the inverter when I noticed the inverter is supposed to have a ground to the van metal. The lug where it is supposed to be is empty so the stray ground wire I found must belong to it.
I talked to a very helpful Tripp Lite tech and it appears that the inverter is toast. I think it is time to upgrade to a pure sine wave inverter.
I put the wires back together and tested the fuse block, adding a fuse one by one and feeling the negative and positive post for heat. I found a couple of circuits that make the positive post hot. I also noticed that by jiggling the fuse board, lights flickered and sometimes went off, then came back on with more jiggling. I made sure all connections were tight.
I'm starting to suspect that the fuse board itself might be bad. I now suspect that it takes more time for the negative post to heat up but eventually it will and by happenstance, the fuse wires touched it, thus melting and bonding causing the shorts.
The Tripp Lite tech suggested that the 8 gauge wire they used for the pos and neg battery connections to the fuse block are much too light and that is the reason they are heating up. He suggested that they should be 4 gauge wires.
I finally found a thread that sounded a lot like my problem in the RV.net forums with the same unit I have (http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/24871727.cfm). That guy had actual charring of fuse board around the negative post. I've sent a message to Randy at http://www.bestconverter.com/ to ask about replacement/upgrade for both the inverter and converter. This guy at this place seems to be highly recommended in several forums so I'm going with the many recommendations.