I have experimented with several techniques for putting cargo in truck beds. I have settled to two primary approaches -- one for barrels, one for crates.
My approach to both does not produce the level of results that we've seen from Troy's work, but the techniques are simple and fast.
I really like to have some trucks with barrels. I make them from the sprues that come in the GHQ individual infantry packs. Just cut up the sprue with a razor, paint it gun-metal, do a little rust washing and light gray dry brushing, and you have barrels.
Most forward troop POL supplying is not done with tanker trucks. It's done with barrels. I often insert some supply requirements into victory points in my scenarios -- ie: you get 2 points for every tank that gets off the end of the board, but only IF you have the POL to support them. You must have 1 barrel of POL per two tanks to get the points.
Here is a Soviet early WW2 POL caravan. There is a medium ZiS truck with nine, a light GAZ truck with six, and a horse-drawn wagon with four barrels.
This posed picture shows many of my civilian vehicles. If you look on the road coming in from the lower right, there is a truck carrying barrels. The truck is a modern Soviet GAZ-66. In this case the barrels are stacked horizontally, rather than standing vertically. I have placed barrels in the backs of several kinds of trucks, including HEMMTs.
With the larger trucks, I often mix the barrles in with crates as well. For crates I just use cut cardboard. Get some modestly thick cardboard, and then slice it to two or three sizes. One longer and flatter, the rest closer to square. I like the simplicity, and the look that the cardboard takes -- no two cuts are actually identical, and when painted, it seems each piece absorbes a different amount of paint. So every crate comes up a slightly different size and color.
I don't seem to have any pics of my crated trucks handy. But there are some crates in this scratch-built artillery emplacement. You can see them in alcoves off of the back of the connecting trench.
One last technique I have used to get a little variety in my trucks, is to grind down the canvas on a select few of the covered truck-backs. This makes them look like an open-backed truck, with a modest load that has been tarped. If you look again to the pickture of the civilian vehicles, there is a GAZ light truck with a "tarped" load coming in from the upper right, next to the van with the white roof.
Just some ideas. Your mileage may vary.
