I do this all the time, my home solar set up is a similar size to yours. Do you run an inverter at all? I have a fairly inexpensive xantrex from the hardware store, it's another expense if you don't have one, but useful to have around. You can get a good fencer that plugs in to 120 for much less money, maybe 80 bucks or so. Run an extension cord out to it.
Yes you lose
energy going from 12 to 120 and then the fencer converts it back again (plus the inverter is on all the time), but it really draws very very little power so I live with it ...it's inexpensive, and it's nice to have the fencer located a bit away from the cabin so you don't have hot fence wire right up to where you live. If you avoid running it through a bunch of wet grass and brush it will draw less.
Another plus if you live where there is winter is that the larger stand alone cabin system will be much more reliable...in January my solar fencer draws right down and stops working..this is the main reason I plug in to the cabin.
A decent solar fencing unit with some kick seems to be at least 250 if not 350 dollars here. I do use one for the far pastures.
I'm going to pick up one of those 120 v meters that logs amps and usage soon, I'll plug the fencer into it and see what it's actually pulling.