I have driven a few times from on property and provided directions numerous times for folks not really sure how to get around on race morning. Seconding John's advice.... get there early and use your car for shelter.
Here are the facts about the morning....
The road into Epcot closes at some point in time. You can watch the race run by from your windshield if you wait too long.
Buses run from 3-4 AM. I would suggest planning on arriving in the parking lot no later than 3:30. You can push back but I have seen traffic back up a few times in the years I have come to the race.
If cold or otherwise inclement weather occurs, come earlier, not later. The line into the lot will back up.
Not sure where you are planning on staying... regardless, do not follow the signs or GPS to Epcot on race morning. The Epcot Dr closes around 1 AM at the intersection of Buena Vista. Plan on arriving and using World Dr. (I can help give general directions if confused).
Fianlly, if cold or rainy give me your cell # so I can locate you in the lot..
Finally, if you have a designated driver, you can sleep in a bit ... they can drop you at the intersection of Bonnet Creek and Vacation Club Way. It is a local kiss and drop spot.
Finally, really this time. Remember where you park. The lot is actually set up for finding cars from the opposite side where the trams run.