There are 3 surviving Mark VIII tanks - 2 American built at Fort Meade (where the Mk VIII unit was based) and Aberdeen. The other is a British built Mk VIII and is at the Tank Museum at Bovington and most certainly is under cover and in pretty good condition. (
Info Tank Mk VIII The International).
The collection at Aberdeen is being moved to Fort Lee in Virginia to an indoor display area. The move is going to take some years to complete. (Moving the K-5 railway gun and the 15" coastal defence gun will be quite difficult.)
Regards,
Charlie