I played the numbers years ago and could not make them work out, Older truck, Service body and crane jib, then the additional tooling for such work as the later crawlers or rubber tired loaders, working Vocational trucks or on highway where would need either the crane or a real dolly to swing hubs off for brakes, seals, bearing failures. Then is AG stuff, never know what will end up on. Just all manner of Heavy, Awkward or filthy.
Need a Dependable chassis, would not be using greater than a 20 year old truck and the service body will necessitate room for Oils, Greases, fuels and a waste oil tank. Along with Welder, Gas Axe, Oxy Lance tooling and severe enough duty clamping equipment to remove gland nuts on cylinders. Then my numbers shot craps. Definitely need shop space as cannot or have less will to work in blowing snows or sheeting rains in a mud or frozen hole.