pressure tank in unheated cabin

Unless you have a special type of modulating pump you will need a pressure tank. In most cases the pressure tank is used to stop the pump from short cycling. If you forgo a pressure tank the pump turn on and off continuously greatly reducing the life expectancy of the pump. Draining it would be recommended if you're not using it and away. If the place is cold you can also use RV Plumbing antifreeze to ensure no residual water freezes. Flush it out when ready to use.

Side note, After reading your other post. Yes you can operate the pump from the breaker with just a pipe connected to nothing. Be careful to not dead head the pump, meaning don't run it with a valve closed. Without a pressure switch to turn it off at high pressure you can hurt the pump or burst a pipe (unlikely but possible)

Yes you can turn the breaker on and fill a drum or pail, whatever you need then turn the breaker off. This would be Similar to flushing the toilet and washing your hands, the pump kicks in fills and shuts off not a short cycle issue at all.