So I made a wall section. I settled on 4"x4" for the floor to give it some stability and to make it fit with my Dwarven Forge Game Tiles.
In the picture below, you can see that I reinforced the back -- gluing a smaller piece of cardboard cross-grain with the larger piece of cardboard. The wall in the back ended up being about 5" tall. I added 3 extra strips of cardboard to the bottom to have plenty of surface area for my hot glue.
The bottom is made of two layers of thin cardboard, glued cross-grain to make the base extra sturdy.
The Model Magic/foam Devil Face is extremely light. I glued it on with white glue. The white stuff is flexible modeling paste. I applied it to fill in some tiny gaps and to give the model a little bit of texture. The Model Magic foam is a little too smooth for my aesthetic taste. :)
|"What foul devilry is this?"
|I think the cleric is contemplating throwing the henchman into the mouth of the Green Devil Face. The paladin stands ready to stop him...
Here you see the finished product. I painted the whole Devil Face in metallic green, then I came back in and drybrushed a bit with olive green and some bright yellow. The "mouth hole" is painted in flat black.
I textured the wall and the floor with flexible modeling paste and I did a black wash to bring out the cracks. It doesn't quite match the Dwarven Forge but so what. :) I think the scale and the effect are both good.
Dwarven Forge Game Tiles are quite thick, so I cut a set of 4x4 and 4x6 "inserts" out of some thin plywood I had lying around. This brings the thin cardboard base up to the level of the Tiles.