Hi,
Do you have a model number for that Cruise Master? We have a 2005 (on a 2004 chassis) and the freshwater capacity is 75 gallons. From the GBM brochure I have for 2004, they used two fresh water tank sizes: 62 gallons or 75 gallons, with the 75 gallon size being used more frequently.
I believe in 1996, the Cruise Master was available with a diesel chassis? Is yours a diesel or gas? When we bought ours, the Cruise Master line was only built on the Ford or WorkHorse gas chassis.
Unless it's one of the shorter (25'-ish feet long) models, I think it's safe to say it would have at least 60 gallons of freshwater.
If you can tell us any more info, I'll see what I can dig up.
~Rick