Nice..
I've seen something similar.
I use to do most of my ammo testing off the roof of my pickup but the trouble is any wind or a slight movement by myself makes it rock. Upon the truck keeps you out of the cowshit and above the crops/long grass and shooting downwards. Nowadays I use a 6x3 piece of plywood to lay on as I mainly test ammo on a permission across the fields not at a range.