How can I defend my home base from invasions?

As you level up, you'll gain access to better blue prints and building materials. Being able to build your housing with stone will definitely help.

Aside from better materials for your house, you can use specific weapons and traps that you can lay around your house. Check the Blueprints section of your Blue Prints and you'll find the following:

Spike Trap/strong]

Trip Wire Trap

Bear Trap

Turret

These items can damage opponents or scare them off, making it effective for protecting your home base. In order to protect your items, you can also build a Safe (Level Requirement 88).