Unless you're hauling bulk building material (plywood, sheetrock, soil, rock, brick, etc) I think a van is likely to be superior on all counts (and if may be superior for non-loose material like plywood and sheetrock still). Anything you can go to the back of a truck for, you can go to the back of a van for, but you can actually have multiple levels of items there if you set it up that way. Anything you would acess over the side of a truck bed should be easily accessed through a side door. A van can also support a small workspace within it, if that benefits your job. Since there's no wind or elements, you can store stuff in open topped containers inside, making access easier while still being secure and secured. You can also get a much larger cargo area in a van that in a work truck of the same size, being it easier to maneuver.

Unless you are top-loading something, there's very few things I can think of that a truck does better than a van. It's certainly possible you have more real world experience than me and can think of some things I'm glossing over though.