Thanks to all for the input. The first sign of trouble was that the Sirus head unit, recently installed at BCS and wired to not require the ignition key to be on ACC (hot wired), did not spring to life. Investigation revealed that the chassis batteries were at 8.5 volts and the fuse from the Echo was blown. Neither of the fuses were a slow blow type, but a standard BUSS fuse, solid metal. After replacing the fuse with a like BUSS 20A fuse we have had no problems. The chassis batteries recharged and there has been no further fuse action. Apparently the "always on" feature, drawing directly from the chassis batteries depleted the two batteries after about 6 hours of radio play, which could only happen if the fuse was blown and prevented recharging from shore power. Power has been very uneven at this park (reason enough to add the VC-50 voltage booster I have been considering) and I am guessing (this is supposition on my part) that the inverter chose to supplement the lack of power with the coach batteries and then when the power returned it kicked on with a vengeance and blew the fuse. The chassis batteries might simply be a separate issue. It's also possibility that the whole bank is "weak" and needs to be replaced. I'm going to replace the fuses with 20A Slow blow types and have the batteries load tested as Fred suggests as soon as I can find someone capable. Until then I'm just monitoring our power usage, crossing my fingers and keeping an eye on the Echo and my replacement fuse supply.