Type I trucks are what you would typically see at a commercial / residential fire. A large wildland or brush unit would be a type III. The engines are not what will be your most difficult design criteria however. A lot of wildland water tenders are built on larger chassis with all axles being drive axles, reworked military vehicles, and other larger trucks with poor turning radii. They also carry up to 3,500 gallons of water, tools, and other equipment pushing them to around 60,000 pounds.
A good reference would be to look at something like an International WorkStar with a front drive axle. That will give you a good idea of the turning radius.