There is a total of 4 pack a punch locations, if you don't know how to turn on pack a punch i'd suggest you watch this video as each of the 4 locations that you activate the pack a punch is where the pack a punch will eventually be.
Now to get onto the achievement. It's an easy achievement really, just that you need to survive the rounds in order to pack a punch at each location. If you placed the pack a punch at the Poop Deck, you'll need to spend 5000 points in order to pack a punch. Eventually (generally 3 rounds) the pack a punch will move to one of the 3 locations i.e. Cargo Hold so all you need to do is use the pack a punch there, wait another 3 rounds and repeat until you've pack a punched a weapon in each location. It counts as well if you're repacking a weapon for 2500 so you can just do this with the same gun (assuming it can be double packed).The pattern on where the pack a punch will spawn is random, so it might take you a few rounds for it to go into every location!
I hope this guide was helpful, this achievement isn't that hard, i'd recommend doing this on easy difficulty as (understandably) you'll have an easier time as you have 200 health and zombies are slower. :p*NOTE* Achievements can't be unlocked if using modifiers, when going for achievements use classic!