Great Lakes Tow Rig Parking

Just call the track and ask.
I would bet they would be able to accommodate you.  I have seen trailers parked in the area to the east of the paddock where the garages are for the track owner and some others.

OK, here's the definitive answer:

Because Gingerman expects a 225-car field (i.e. Every nook and cranny gets filled) for the SCCA Majors weekend July 5-8, if you want to a drop a trailer, you will be able to do so in the side field. You will have to talk to Marybeth or Mary and let one of them know during the race weekend that you need to leave your trailer. You'll have to sign a release and follow directions and please be nice because the people at Gingerman are awesome.

You shouldn't have any trouble retrieving your trailer on July 7, but do know that the paddock will be busy with a large race weekend so you will have to negotiate lots of people and cars to get out of the track.

ALSO—and this will be in official communications soon—the rally is no longer ending at Gingerman because of the aforementioned space restraints. We will be meeting at the shelter at Van Buren State Park just south of South Haven. No alcohol is allowed at Van Buren, so you'll have to take your celebratory drinking elsewhere. Sorry, that's where the space was; there will be ample watering holes in South Haven after the 6 pm awards.

We will still be departing Gingerman on Monday morning, however. Lemme know if you have any questions.