Hey guys,
Just going to write a short guide on how to get Perkaholics and Pack addict the easy way with 3 players.
Waves 1-5:
Pretty simple first few rounds just kill zombie's with pistol and knife to get maxium pionts, You will defitinitly get Max ammo, Insta kill and a Nuke to help you out, When you hear the sound for dogs open up the right side leading to the Thompson and buy it (Duh

) and take out the dogs.
Waves 5-11:
After you have messed up Fido and his buddys remove the Debri from the stairs, turn on the electric and random if you must, But dont buy any perks yet (You will survive trust me) Know just camp in the area with the Random box with your back against the big door to the Teleporter stay there and just rack up your pionts.
Your in a pretty big area with ampel space to move and zombies can only come at you from one place, You should get Dogs at round 10, Mess up the dogs, Now you must get a Crawler or the last Zombie a the end of round 11, Now its time to power up all Teleporters, Get Jugganog (Only if your not getting Perkaholics) You will have more than enough money to get Perks, Randoms and maybe an Upgrade, Now make your way to the Teleporter room next to the Pack a Punch.
Waves 11-20:
Now your in the room with the teleporter the person wanting Perkaholics goes to the little room next to the Teleporter (Mp40 is in here so i recomend getting one upgraded for ease of the ammo) there's only one opening to watch and you can keep boarding it up, The other 2 players stand outside the room, 1 on the far side watching the Hole in the wall and the other stood next to the room at the top of the stairs taking the Doorway.
Keep a zombie at the end of Every round to get to the Random box and Pack a Punch. In these rounds this is where your going to get Pack addict just keep a main Weapon Ie: Ray gun/MG42 Etc. and have a back up that you dont mind getting rid of because at the end of every round you will have enough to get a Random and upgrade it. Then just come back to this room and repeat.
Waves: 20-Onwards:
Now the guy going Perkaholics will have it so at the end of round 20 grab Perks, Also you all should have gotten Pack addict by now because you get more than enough money, If not keep playing staying in the same area till you get it, Then just back out and restart switching up who gets the achievement.
Me and the other guys i play with was doing this method for a few games with perks and we got to Round 23+ like 6 times, Then on our first try with me not getting any Perks we got to Round 25 and i got the Perkaholics and they both got Pack-Addict. Not as hard as people think if you just use abit of planning and have some good players that know what there doing.
I got downed on round 19 and my friend got me up and when the round ended i got the achievement, Not sure if you can die but i presume you can.
Not a real in depth guide but you get idea on where you have to go and what to do

Hope this helps.