A lot of departments use small 4x4 squads, which carry a small amount of water (around 200 gal) but also serve as a utility unit. They tow trailers, and carry basic rescue tools and sometimes have rescue equipment such as winches.
My idea would be to add something similar in the game, that acts as both a utility (rescue capabilities and trailer towing) and a brush unit (off-road capability, small water tank and hoses).