The basic foundation of an easily drained water supply system is to build it on the same principles that a waste-water system follows - every pipe, consistently and without fail slopes to the drain location. It may be beneficial to add a few vacuum relief valves (sold for a code requirement on water heaters, typically) to vent the pipes when draining.
Though, in the age of PEX, a common enough approach is to worry less about the pipes freezing, if they are PEX.
Standard approach for a location with power is to insulate the pipe well and install electric heating for the pipes. The cheap junk with a separate thermostat is what's usually on offer at the hardware store, and fails a lot. The better version self-regulates on the outside of the pipe. The best version of those goes inside the pipe. The first-time cost runs as expected (increasing) from worst to best. The longer term cost runs as expected (decreasing) from worst to best. Cheap is expensive in the long run.
If you wanted to use a frost-free hydrant as your feed, you'd probably want a hose quick-connect on it, with a short hose connecting to the plumbing, and all the plumbing sloped to the that point. Disconnect the hose and drain the pipes into a bucket, while the hydrant drains into the ground below.
You could cobble up something to mimic the operation of a frost-free hydrant with a below-frost-line electrically operated 3-way valve, and at least one check valve (on the drain port, to prevent things from contaminating the supply through the drain port.) You might have a have a fun time digging it up when the mice/voles/moles/shrews chew the wires for you in mid-winter. I'd choose a big lever and a rod , (quite similar to the FFH handle) and a manually operated 3-way down the hole; the handle could be concealed in a wall cupboard somewhere (or be outside the cabin) if you find it visually jarring. Or perhaps use a set of moose antlers on the wall that you rotate as the lever.
Draining the entirety of the cabin plumbing there will either be no problem if the percolation is good, (typical of gravel) or a big problem if the percolation is not so good (typical of clay soil.) The frost-free hydrant approach you're only draining the riser tube, which is quite a bit less water. Perhaps bury a perforated drain pipe leading away from the valve box while you're digging to take the drainage water and give it space to percolate from without backing up the pipe.
If there's a water heater in this cabin the drain volume gets potentially much larger, (I suppose it might be a propane tankless and not much volume) and you have to ensure that the heater never turns on when it's not full of water.
