[Richard]

For sure , I wonder if driving the coach to my storage place with frozen batteries could damage my alternator ?

 Possibly, but why take the chance. 

If you removed the frozen batteries and installed any 12V battery for the chassis, you would protect the alternator and have 12V to run the engine electronics. Of course, you would have to get a jump start at the shop to get it cranked.

[77newell]

Richard's recommendation is spot on in my opinion, except for possibly one teensy thing. The batteries on my 77 coach froze solid with bulging sides when I owned it years ago. After I thawed the batteries I alternated trying to slowlycharge them and doing the desulphation routine. The sides never completely straightened but the batteries worked fine for another 4 years. You won't know til you try. Sometimes miracles do occur. I didn't think it would work, but trying was essentially free, so I gave it a shot. With a smart charger that won't charge into a shorted battery I had to take my time with the smallest charge rate since the charger thought it was shorted because the battery was so flat.