Any thoughts on the feasability of keeping batteries in the crawl space? Since the cabin will be vacant in the winter ...
I wouldn't even consider putting them in the crawl space OR indoors.
- They'll have to be float-charged - or they'll discharge, sulphate, and die over a few months. Float-chaging can make them outgass - much more so if something goes wrong with the charge controller and you're not there to catch it.
- They produce not just explosive gasses but small amounts of corrosive and toxic vapor. Not only could they blow up your cabin, they could rot out the plumbing and wiring.
- They have to be readily accessable for fluid level checking and maintainence. There's a risk of spilling acid on yourself or having a short throwing molten metal and maybe starting a fire when doing thi,s even in the best of situations. You DON'T want that happening when you're in the crawl space.
If I didn't have an enclosed garage to keep 'em in (in box against the wall sealed against building air and vented to the outside top and bottom) I'd be inclined to put them in a small insulated box or building - a shed attached to the outside of the house or (better yet) separated from it by at least eight times its height, so flames won't be likely to spread to the house if it catches fire. (You don't want it TOO far away because you'll need heavy wire from the batteries to your cabin's load.)
If they're receiving a non-trivial amount of charging and discharging they'll be putting out heat. Insulate the box and they'll stay warm. Just use ordinary siding and household fiberglass insulation - and I'd put a layer of drywall on it if the insulation is paperbacked, to protect it from fire if there's a spark.
You can put in a thermostat to turn on a couple small automotive lightbulbs - two or more for redundancy from burnout - to keep the batteries from freezing up in a DEEP cold snap. But if they're kept charged the acid also serves as an antifreeze.
Put the batteries on a small rack above the dirt/slab floor to allow air to circulate all around them and prevent temperature gradients between the top and bottom of the battery.
(Please note that this is from my understanding of the theory of how this should be done. I don't have direct experience with a battery bank of my own. But I'm sure someone else on the board will correct me if I'm giving your wrong, or excessively elaborate and expensive, advice.)