By now you've had some good input, but also consider your topography and majority of wildland incident types in doing this. Here in Central Louisiana, our coverage area ranges from Forest, Pasture, and Lowlands. We cover the lower portion of the Kischatee National Forest as well. To meet all these variables, we run 2 Type six (dual wheeled) units with 300 gallons. (Single wheel) 1-3/4 ton 4x4 with 300 gallon skid unit and foam. 2-1/2 ton 4x4's with 125 gallon tanks and a 4x4 ATV Mule with a 20 gallon CAF Unit. Most of our calls are "Low burners", but always consider all the possiblities. We had "West coast" type burns in the drought years in 2000-2001, so also look at equipment requirements involved in working with a Task Force or Strike Team. Good luck and keep safe! Jim
We use an old single wheel 3/4 ton from the 70's with 150 gallons and a Mad Dog unit for our normal brush firefighting system. The Mad Dog is a high pressure, low flow system that is kick ass on about 99% of our brush fires. This truck also has a standard pto pump and a few hundred feet of 1.5" for larger fires and to have drafting capability. Most of the departments around here have switched to Mad Dog type brush units. The water lasts a long time and they are very effective at putting out fires. There is also foam capability with these units as well.
My opinion is that you simply can't put the fire out if you can't get to it! Dual wheels are terrible in mud and they make the truck harder to maneuver around. Keep the vehicle as light as possible while still being able to fight a lot of fire. We usually can take our brush unit into many places that newer, bigger trucks simply won't make it. We also don't care about dings, dents, and scratches! This is a real brush unit, not a parade piece.