Well, as it may not directly "make" money, then it is at least income-offsetting:
Calculate the cost of delivery of those materials against the "savings" by using ones own vehicle (total cpm + hourly wage of you as owner). It is "cheating" to count one's own time as free or at minimum wage.
The value of the truck needs to be more than convenience to come up with a figure which makes sense to allow sinking money into it.
What is the current sale value of the truck?
What is the cost of upgrades?
How long will it be kept?
How many miles will it cover?
Versus having materials delivered and snow-plowing done in another fashion (or by another person), how often does the new bed in consideration have to be used to pay it off?
Then, and only then, do mpg-enhancements make sense.
I don't do any snow plowing (or climate comparable), so a dump trailer makes more sense to me. I know it can be a money-maker, and there are always buyers. In any event a truck bed or a trailer used locally/regionally is more about seeing to
rolling efficiency than to aero qualities. More money to be saved, as well, by engine efficiency and route planning efforts.