Instructions
Move into or create a house a house for your Sim. Any house in the game can be adjusted to become a full base of isolation.
Stock up on as much food as possible. Once the base is complete, the grocery man will be unable to reach your house. To ensure your Sim's survival, buy multiple fridges and store them in an extra bedroom to keep your Sim fed for a lifetime.
Dig a moat around the house. To do this, access the Construction Mode (F3) and insert a swimming pool around the house's land. Completely surround the base-to-be, making it impossible to get to. You can make the moat as skinny or wide as you like.
Remove all doors that lead to the outside of the house. If any Sim is brave enough to traverse the moat to your house, they still won't be able to enter the house and speak to your Sim if a door leading inside does not exist. This is important, because bill collectors will not be able to evict you from your house, even weeks after not making your payments.