It's been a while, but is it definite that they move the car on the day of the storm in the first one? Marty1 is there for what, a week? And the DeLoreon is one of the first things he shows Doc, with it then being in his lab in future scenes (like when Loraine visits to ask him to the dance). Either my memory on the timescale is screwed, or the car had already been moved a few days before Marty2 arrived on the morning of the storm.
l mean, why, once he'd had the machine proven to him, would Doc leave it in the open when he has a garage (plus either ownership or ability to rent a tow truck of some sort to move it about)?