First of all, what stuff do you need? For mine I used some polystyrene, just the stuff you get in packaging kitchen supplies etc. You will also need PVA glue, the right hand of kings. You will need something to act as the cladding, I used coffee stirrers because they are cheap and plentiful, which I purchased here. I used a normal pair of modelling clippers to cut them up. One other important thing you will need is a hot wire cutter for cutting the polystyrene. You could make one, shown with the pic of the big wooden frame above made by Nate Zettle and kindly loaned to me, or you could buy one, like my plastic thing below. It's much easier to get straight lines with the one above, because it's fixed.
First thing you will need to do is make some polystyrene cubes. I am making the crates for Malifaux so I would recommend 1" cubes because the height of the terrain will then simply be how high you stack them.
next you will need to cut your coffee stirrers into 1" lengths. Don't cut them all up, you will need slightly longer ones later.
next simply PVA your sticks to the polystyrene, like shown in the picture below.
Finally, attach the last of your sticks perpendicular to the ones that are already there, but only a couple on each facing.
And there we have it, some crates ready for painting!
Honestly I think it's easy, but my girlfriend said that she would not have thought of doing it so it was worth posting a blog post about it. Hope it's useful to somebody.