I added a leaf to my rear suspension in my Transit Connect after a few years of use tired the original ones out a little. I paid it off after five years last December and I don't regret getting it at all. While other guys were spending $10k or more on fuel per year, I was cruising along for less than $6k. That's not a wimpy difference.
There's a principle at work here that goes beyond wimpy or heavy duty. When you look at efficiency, traditional US trucks suck in every respect. They weigh a lot, they use a lot of fuel just to haul around all the weight they need to qualify as "heavy duty," the suspension, brakes, engines and basically the whole vehicle is rarely if ever used to it's maximum capacity. Efficiency is usually considered good when you're using above 90% of what something is designed for. So if you have 10 million trucks on the road running at 35% of their rated load, you're wasting fuel and the materials that went into making the vehicle. Swap out those 10 million trucks for "wimpy" European ones that are running at 90% or more of what they were designed to do, and you're getting your money's worth out of them and using a lot less fuel to do it. Millions of gallons less fuel per day at the national scale.
So if you need to carry 3000 lbs of tools and materials on a regular basis, by all means get a box truck. It's the appropriate vehicle for that.