Short-term storage

That would be fine, but you should put a maintainer on the 12 volt, or disconnect the negative cable

 

You can buy a charger to keep the hybrid battery pack fully charged and balanced... Or you could switch to lithium or sodium chemistry that doesn't have the self discharge problem that NiMH cells have in OEM pack.

But given the engine problems that Gen3 Prius have, you're probably better off selling it while its still in good condition and buy an old truck that doesn't have these hassles and has more uses as a rarely driven vehicle. It's just a matter of time before everyone will be more aware of Gen3 engine failure problems and the re-sale value of the Gen3 prius will fall in big ways.

 

If your driving it a few times a month and about 250 miles - IMHO, should be enough exercise for it.
1. put an automatic battery maintainer/RV battery charger on the 12V
2. I would probably do some sort of mouse deterrent strategy for the car - so they won't chew on the wires and turn it into a mouse house.

Good Luck...

 

250 miles a month is 3,000 miles a year.
For some people that's 'normal use.'

You're worried about the Traction (hybrid) battery but Priuses have really poor 12v batteries, so that's probably where I would focus my attentions.
I'm presuming that you've read all the threads and know all the things about the head gasket issues - so be sure and keep an eye on your coolant.

Your car is 13 years old and anyone with kids knows that's when they start acting out....