I have had huge freezing problems. I think it was me that alerted SMB to the fact that it's NOT safe to have water freeze in the heat exchangers. Maybe we should call that one "Ken's Recall." This pic is my Flatplate after I owned the system for two weeks. I only found the bulge in it because I uninstalled it to put it inside. My connections had cracked, which is why I was doing it.
So, I'll take this in quick parts:
1. Heat exchanger. I strongly argue that it is not acceptable for winter camping to have this outside. Not only to you have to go out in snowstorms to drain/fill, but if you forget to drain, and water freezes in there, it might rupture or cause a small leak between your (poisonous) ethylene glycol solution and your drinking water. Or it might not. This is exactly why SMB did the recall, added the valves, and went with a double wall exchanger. The problem is, if you forget to drain and it freezes... is it still safe? After the first freeze? Second? Third? Then you never know if you're slowly drinking undetectable amts of poison over time. That is not acceptable IMO. Of course, if you never let it freeze and always drain it, then you're fine. But draining it 2-3 times a day is not the convenience that I wanted.
Here's a pic of my flatplate moved inside, under the sink, and insulated. The black cylinder is an accumulator to keep the pump from constantly going on and off. Figured I might as well do it right (credit to the Badgers on that one).
2. Water tank. I had mine freeze, WHILE WE WERE SLEEPING IN THE VAN. Yes, the heater was on, but the water tank is on the floor. And it was cold out (Kirkwood, CA). And the hinged door was completely removed (so that skis could poke through). Water tank bottom froze, water lines on floor froze, and I think it did some minor damage to the pump as well? So, when I redid the water system and moved the heat exchanger inside, I put 1/4" of ethefoam under the tank, and that did the trick. Also moved my water lines off the floor (duh), kept them from contact with the metal sofa frame (duh), etc.
Here are all the left over PEX parts after I did my install. It really simplifies the system. Now that there are the extra drain valves, as delivered it's probably even more complicated.
Summary: as delivered, the SMB is fine for occasional not so cold camping, or one or two trips to the mountains in the winter. But if you're going to live in it skiing every weekend, it is not done properly. My guess is most people who buy SMBs just aren't into that kind of cold weather suffering!
--------------
Addendum: SMB won't put the flatplate inside the van because they consider THAT a safety hazard. They had one other model break in a van, spraying boiling hot engine coolant around, and generally wrecking a lot of the cabinets. I would argue that with a simply injection mold, one could make an outer "holding tank and spray shield" that would prevent this from happening (my locating under the sink and with insulation is my effective spray shield; I have no holding tank/tray though). Thus, I see the valves outside as a bandaid vs the right solution. Again, if you're not a constant, extreme cold weather camper, this isn't really an issue.