How To Survive 2

Edit: Apparently this is NOT exclusively a host only achievement. Refer to the comments below this solution

Important: It has to be YOUR camp for you to get an achievement for this.
I played through the entire game in Co-Op in a friend's camp, I still had to level up my own camp. Be aware of this.

This achievement (if done correctly) Will also unlock 3 additional achievements, for completing all 8 of Kovac's challenges, while keeping the Pylon from taking damage during the defence sequences.
If you ever miss one, just re-do the defence sequences where your pylon took damage.
Now about this achievement:

Obviously levelling up the camp speaks for itself: Get the camp to the maximum level (51).

This, however is not simply done by pumping all your xp on your camp.
Along the way you will have to complete 8 camp defence sequences.
The first of which being at camp level 10, and the last being at camp level 50.

Picking your camp location is very important. Refer to the screenshots below.
Spot A and B are popular picks, however I strongly recommend going with the best one as marked on the images provided.

http://imgur.com/a/aSAbr

Additional info:
Buildings create a "Safe zone". This causes zombies to never spawn right next to your buildings, so try to spread out your buildings, or maybe even place a few you don't need, to make sure NO zombies spawn inside the perimeter of your camp.

Zombies slow down when climbing a low wall. Combine low walls and rotating arm traps to slow down the zombies drastically, saving both your rotating arm durability (In a defense sequence, as it will take longer for the zombies to reach traps, therefore fewer spawns over the course of the 5 minute sequence at camp level 50) and also generally making it safer, as the zombies will be exposed to the arm traps for a longer period of time.

Make sure to always collect wood, as you'll need a lot of it to build up your defences.