Yeah, it is a wheel well, I'm thinking maybe the idea was to use wood to try and keep the noise from rocks banging against metal to a minimum. I thought I read somewhere that they did this so that they could keep the box at a height lower like the 1/2 tons as well as I think the box is a bit wider than the 1/2 & 3/4 tons?, so keeping the box height lower and using larger tires required this design for the tires to sit in the well a little.
