You must have a strong back!!
My 2 batteries are out on the tongue of my trailer in my driveway.
I've got a battery tender JR on there. It's actually plugged into my flag pole
spot light timer so it's on about 6 hours a night. It wouldn't hurt if it was
on 24/7 as the battery tender is automatic and will shut off when the
charge is topped off.
Unless you have security/theft worries or don't have 120v available
I see no reason to bring in the batteries IF you can keep them charged
where they are.
They won't catch cold out there--- honest!