It's not just building an encampment, it's running the district project "Encampment Training" which will give you GPPs.
Early game on online speed you can complete one of these projects in 2-4 turns and get at least 10 GPPs. Play as Japan and build 2 encampments and have each one do a district project and you'll beat everyone to the first GG and be on your way to the 2nd one. Of course, this means building fewer military units, settlers, builders - it becomes a bit of an all-in play.