I have redone the interior from the feedback, as the outer edges were just planes meaning that it wouldn't look very good in the game engine so I added extra geometry to thicken the sides out more.

Here I have extruded the back out then resized it a little smaller that the original in order to create a small edge in order to make it have a small curve to try and make it look less blocked and more rounded.

Finally I have rescaled the actual forklifts main body in order to have it the correct size as it look squashed and small compared to the forks.