SyncroHead@aol.com wrote in reference to the solid state coach battery 
blocks:
 "They have an inherent voltage drop across their internal diodes that 
prevents the battery from becomming completely charged."   

 Thanks for the good tip.  I just went out and measured one, and it drops 
.6 volts, just as you suggested.  I agree that the the charge rate to the 
coach battery would be slowed, but since there's easily more than .6 
volts to spare with a healthy alternator charging system over the 100% 
full charge 12 volt battery voltage, I'd think that it would ultimately 
get fully charged, though slower.  That's assuming the alternator can 
"see" the load as a partially discharged battery.  I'm not sure.  Just 
how will a standard charging system respond to a .6 volt demand impaired 
coach battery?
  Anyway, I'm convinced that the relay is a better controling device, and 
my solid state box will never be installed by me.  Thanks again.
  John Wakefield