Have you thought about not using shelving?
When acquiring equipment, our philosophy was: if we need it once, we will probably need it again, so buy it. It has been a long time since we needed to buy anything new, but the approach produced a larger collection of equipment than you see on most straight trucks. None of it is stored on shelves.
Shipping cases on wheels store the items we use less frequently. An open-top box sits on top of the shipping cases to store the frequently-used stuff. Furniture pads are folded, stacked and strapped onto a furniture dolly. For small jobs, four pads sit loose and handy on top of the stack. Straps are kept in plastic buckets that sit on the floor between the cases and pads. Load bars (E-track shoring beams) keep everything in place. The pallet jack, hand truck and tripod dolly sit out where we can get at them and are strapped to the walls.
There is more but that gives you a sense. The idea is to mount everything on wheels. The box is 16 feet long. If we get an odd-ball WG piece of freight that is 16 feet long but not too wide, we can move the gear to the sides in an instant. That generally does not happen since we are in a CR-unit and the offers are usually limited to 12 feet. If necessary, we can move all gear forward in a a couple minutes to provide 14 feet of full-width space for freight. Our carrier knows we have 14 feet of usable space.
The huge advantage of having your gear on wheels is cleaning. It is a piece of cake to move the gear aside or out of the truck to clean the back.
Storing furniture pads on wheels also makes it a breeze to wheel the pads inside a building if you need to pad wrap a number of pieces before moving them to the truck; or to wheel them into a landromat if you want to wash them.
Keeping permanent shelving out of the truck also makes it easy for technicians to get at the reefer components and plumbing if they need to.
Ours is a reefer truck. Reefers produce condensation. To help dry the truck after a reefer load, beams at the front of the truck create a 2" space between the front wall and the equipment. The equipment rests against the beams, not the wall. That and the wheels the equipment sits on provides good air flow over the top, bottom, front side and back side of the equipment.
Finally, with no shelving built into the truck, you save that weight.
I am not at my own computer now. When I get back to it, I will attach a photo of our no-shelf technique.
Shelving built into the front of the truck is a common technique that has served people well for many years. We went with no shelves for the reasons stated above.