Mongoose armies come with their own plastic bases - 25mm by 50mm for infantry, and 50mm by 50mm for chariots. I popped the figures from my temporary bases using a small screwdriver, and glued them to the Mongoose bases using a combination of white glue (on the bases) and superglue (on the figures).
I painted the edges of bases medium brown.
After the paint was dry, I applied some watered-down white glue on top of the bases, and dipped them in my terrain box. I have an already-prepared bottle of watered-down white glue at about a 50:50 ratio, and keep my terrain in a cigar box. My ground terrain consists of real dirt and model railroad ballast of various colors and sizes.
After that was dry (about 30 minutes), I brushed on some more watered-down white glue here and there, and dipped the bases in my other terrain box that contains various flocks, static grass, etc.