I found a toy lorry on Ebay, bought it for £10 and got converting. I chopped off the spoiler and used it to lengthen the wheelbase of the cab. Most of the rest of the work was bits of sprue and plasticard. I made a false new grille out of plasticard and curved bits of sprue and blended it in with green stuff so as to lengthen the bonnet/hood. The air intakes were made from those smoke launchers you get on Games Workshop tanks.
Not bad, but it needed a trailer to pull. The model came with a suitable plastic trailer, complete with some kind of buzzer that you could fit batteries into to make a sound, which probably delighted small children circa 1982. I never found out what the sound was. Another voice lost to the Wasteland.
Again, this is just a plasticard job. The car on the right is a Matchbox or Hot Wheels car, so you can see the scale. It's hard to make out in this picture, but there's a plasticard superstructure on the front of the trailer, which is supposed to look like half a VW Beetle, as per the film. I went for a blue-black colour rather than straight black.
I added a second plasticard Beetle and some pennants to the back of the trailer. One of these days, I'll use some spare wheels and a ping-pong ball to make the fuel pod that gets pulled along behind the rig at the start of the film. But for now it's ready to strike down the unroadworthy! Do you see me, Toecutter?