I'm sorry to hear of your troubles and can tell you that I'm more than feel your pain. I had a very similar thing happened to me three times now.
As my profile says, I have a 2000 33 ft flat nose rear engine IC. One day I drove it around and parked it in front of my house. An hour later I went to start it and it was dead. Turned out in my rear electrical panel tucked between a whole bundle of wires and wrapped up in tape and then covered in plastic was a diode the size of a grain of rice. The lead on that diode had broken and it shut down the whole bus. Very lucky that we found that.
Jump ahead several months later to last Tuesday. After months of the bus running just fine starting just fine everything just fine, I went to a store and when I came out again the bus was dead. Same exact symptoms. This time it was start relay. We changed the relay and everything started up and was fine. 2 days later, this last Thursday, I took off for my first road trip in 2 hours later broke down. After 2 days of troubleshooting with the help of many people I was able to get the best started. If them broke in on 10 miles later on the side of a busy freeway and is now at the international dealer.
What happens in my situation is I get water and fuel light comes on, we're normally I get the way to start light. According to a mechanic those are two completely different circuits. It appears that when the ECM does not get power, the wait to start light does not activate and the water and fuel light comes on. The minute the ECM receives power, all is fine. Unfortunately, in my situation as you start driving something happens in the ECM loses power and everything stops.
I get the same clicking on my driver side front panel, but nothing else.
If I jump my start relay it does crank, but no signs of it starting. Again, this is because the ECM is not getting any power and so it not telling everything to go.
Just some place for you to at least start looking.