Gramps seen in article in woodworking magazine that used 4" (i think) PVC. He cut them about 12" long and then cut a slot along the bottom side so the drill can be "holstered" into it. He drove a couple wood screws through the "top" of the PVC into the bottom of the shelf above it to hold it in place so now he has a row of PVC holsters that all his cordless drills slide into.
If your going to do this on a work van, I would make a mount so the PVC is angled at a downward angle so they cant slide out while traveling.
I'll see if I can find some sort of picture of them online so this makes sense, but it's cheap, easy and works perfectly.
here ya go: