It might be easiest and simplest to put the lid and the coal bin in the cab, or tied down in the bed. Maybe some blankets to wrap that stuff up. If you do that, you might be able to just lay the thing down in the bed for more stability. And make sure you have a strap to hold down the hinged lid so that doesn't take off on you. If the tank is missing, make sure you have some string or rope to keep the regulator from flopping around too much.
Good luck on closing up the deal, and we hope to congratulate you soon on your new SS! They are truly a thing of beauty, the height of the Weber art.