If your chassis battery is checking out good and I suspect it is since this is intermittent. I would look at the relay that ties the coach battery to the chassis battery. They must break the main line to insert the coach battery in parallel before the starter or the solinoid. I dont know exactly how they wire it but I bet there is a black box where the chassis and coach battery go in and a single line to the solinoid comes out. If the connections are tight there the problem has to be that box.
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