I would like to thank you all so much for all the advice and encouragement at my time of need! The mechanic did return, and although his competency may be a little questionable, I cannot fault his enthusiasm and his honesty. He finally declared that the 'Big Boy' had been wired in reverse which made it constanly draw current from the chasis batteries. I must confirm that the BB was getting very hot, indicating constant use. The BB was disconnected,, and the chasis batteries were charged sufficiently from an external source to allow the engine to be started. I allowed the engine to run for over an hour, stopped and successfully restarted it. We are, as planned, to return home tomorrow, and it was agreed that the mechanic would return if needed to get us on our way. I will, of course, take up the problem, whatever it is, with a mechanic I have the utmost confidence in on reaching home.
Again, fellow Beavers and journeymen, my sicere thanks.