I got this idea from someone, somewhere out there on the internet, I just can't remember where or who....Anyway it's quite a simple idea really- the best ones often are.
Why spend ages messing about with modelling clay or fork out for commercially made craters for your battlefield when you can use the humble tin foil container?
Mine were made from custard tart containers. Simply turn them upside down, trim that lip off, cut an approriately sized bit of foamcore or card, glue it to the base upside down & squish the bit in the middle down. It looks cunningly crater like already...Once glue dries coat the thing in PVA and cover it in some gritty sand. After that has dried start applying earthy coloured paint, getting progressively lighter in the coats, & finally add a wee bit of flock around the edges. There you have it, do yourself a favour and give it a go. Mine also doubles as a percussion instrument because some sand got trapped underneath- shake that crater :)