I don't believe the AMEX collision coverage, in lieu of the rental car company's CDW, covers the Ford Expedition (smaller than the gargantuan Excursion) either. I had a similar experience with Budget at CVG a couple of years ago. There were no mid-size cars on the lot so they offered me an Expedition at no extra charge.

That thing was huge! I was not at all comforatble with the Expedition. Fortunately, I was able to drive it safely and there was no damage to the Expedition when I returned it. When I got back to Chicago, I called AMEX and learned that they do not cover the Expedition. I was so relieved that nothing had happened to that thing and I never want to rent one again. It's just too much. I can't imagine what driving an Excursion would be like!