Yes you can lawfully armor the vehichle but practically is another matter.

If you just want to protect the driver it cam be done simply without too much weight but if you want to armor the entire rig on all six sides not too practical.

One method that is effective and inexpensive is sand, all you need is 6inches of dry sand or pea gravel to stop a 308, use the sheet metal for the exterior form and usb/chip interior, only have to be 24 inches high off the floor, just enough to shield a crouch position.

The Afghannies would spread the door panels and poor loose gravel in them for driver side protection.

1/2" thick ALGOTUF steel plate will stop 50 bmg rounds unless it is AP at 2foot distance.