When is the best time to scavenge an outpost?

It is recommended NOT to scavenge any outpost early in the game since they’ll provide you a safe haven where you can conveniently fast-travel and give you access to helpful facilities like Workbenches, Garages, Boathouses, and Helipads. Having many liberated outposts will also make it convenient to back hijacked ethanol tanker trucks.

It’s not recommended to scavenge an outpost early in the game unless you have access to higher ranked weapons and companions. Imagine not being able to take back an outpost because you don't have the proper weapons, perks, and companions to deal with the stronger highwaymen guarding the place. Ideally, the best time to start scavenging outposts is when you have access to same-level or higher ranked weapons, or when you’re in dire need of more ethanol.

Once you have access to the Elite-ranked weapons, you’ll need more ethanol to upgrade them to further increase their damage. At that time, you’ll need to scavenge and liberate high-difficulty outposts to efficiently get the ethanol needed. Completing a Rank 3 outpost undetected will yield 450 per run or 375 if you're detected but no alarms were triggered. (300 default + 150 or 75 bonus ethanol, respectively)