Learning and rethinking my cabin power system

I am not aware of any problems with the marine disconnects, when they are from a good company and sized correctly.  I've used tons of them on DC installations, both in smaller Alt Energy applications and on boats.  Most of the heating of electrical equipment happens when you push it above 90% of its rating. You won't be getting close to that.  I am not pushing the switch over James recommendation, just replying to your question.

I like his recommendation of the igloo cooler. I don't remember where your cabin is, but have the impression that it gets cold there in the winter. I was going to ask where exactly you are going to put the batteries and how cold you would expect that area to get in the winter.

When you say 4 AWT I am assuming you mean 4/0, not 4 AWG.  I’ve seen that terminology from a couple of “inverter stores”. It’s a bit of a sore point with me. 4/0 is “four aught” or sometimes “ought”. It means four zeros.  Call me old fashioned if you wish, but I can’t help but wonder how much they know, if they don’t even get the name right.

Jerry:
I am not the best person to ask about real cold weather for long durations, and batteries (California). Perhaps someone with more cold weather experience will jump in here.

What I can tell you is that I do not like to see a working battery get below about 50 degrees internal temp. The batteries have a large thermal mass, so they do not change temps rapidly. Using an insulated battery box helps keep the ambient temp extremes (hot or cold) from affecting the internal temp too much.
The float charge and the insulated box will help, but I would still expect the battery temp to drop over time. If you do make a snow trip, you would need to treat the battery as cold, even though you may have heated the cabin to warm and toasty.

The other topic that I'll toss at you is the box venting. I would give some thought to venting the box outside the cabin. While that may raise some cold weather issues, I would not want a battery bank venting fumes and H2 into the living space of a small cabin. During warm weather, heavy battery use, equalizing charges, etc, you can get a fair amount. The smaller your cabin is, the larger this issue would become.

Ken