From Wikipedia:
The motorhomes were built in either 23-foot (7.0 m) or 26-foot (7.9 m) length, with about 90% of the total production being the latter. The wheelbase from the front wheels to the centerline of the rear tandem pairs is 140 inches (360 cm) for the 23-foot (7.0 m) coach and 160 inches (410 cm) for the 26-foot (7.9 m) coach. All GMC Motorhomes are 96 inches (240 cm) wide and about 9 feet (2.7 m) tall including the usually-installed roof air conditioner. Interior head room is 76 inches (190 cm).
Gross vehicle weight rating for the 23-foot (7.0 m) coach was 10,500 pounds (4,800 kg) and 12,500 pounds (5,700 kg) for the 26-foot (7.9 m) coach. Most GMCs with factory interiors have a 30 US gallons (110 l) freshwater tank and a 30 US gallons (110 l) holding tank.