I've just made a challenge using my "4c-Tranquil" map. The file attached is the map with the challenge included in it, so you just put it into the maps directory and the challenge should appear in the list.
The scavengers in the middle supply you with enough peace time to build up and develop your base, but if you want to beat the challenge quickly enough, you'd have to take the initiative yourself.
Am i doing everything correctly? Won't such files cause any kicking problems, like map-mods did? If it's all right, i'll bundle some challenges with other maps of mine.