"Amongst all possible ways to build Moonbase, 1-crystal build arguably requires the least amount of efforts and the build itself is very stable. Do note that it is possible to defend all 3 crystals simultaneously, however, that will mean more building, more maintenance and a larger area to cover when you loot.

Build layouts:
Build phase 1 (before wave 5): http://puu.sh/bCr4S/acb6fd9b23.png
Build phase 2 (before wave 6): http://puu.sh/bCr6L/9b829cb4c3.png

Useful links:
My DDE guide on Trendy forum - https://www.dungeondefenders.com/eternity/guides/113635
My Steam guides - http://steamcommunity.com/id/zodthereaper/myworkshopfiles/?section=guides&appid=65800
My Steam profile - http://steamcommunity.com/id/zodthereaper/
I'm the founder & admin of the largest non-official DD Steam group - DDFreeRunsByRequest (http://steamcommunity.com/groups/ddfrbr). We do free runs for the community and we help out new players. It's a public group. Feel free to join and check it out yourself."