Here is what I experienced when going from a 1991 27' Tioga class C to a 1995 33' Bounder class A.
Class C E350 460 Ford 10,000lbs
30 Gallon fresh water tank
36 Gallon fuel tank. Average 9mpg
20 Gallon gray water tank
20 Gallon Black water tank
1 12 volt group 24 house battery. No room to add more under hood.
18 Gallon propane tank
Class A F53 460 Ford 17,000lbs
100 Gallon fresh water tank
75 Gallon fuel tank. Average 7mpg
50 Gallon gray water tank
50 Gallon black water tank
2-6 volt golf cart batteries. Room to add two more behind front bumper.
24 Gallon propane tank.
If you plan on spending any time off grid, tank capacities are important.
Richard