I've spent the last few days remaking the coop airlock/checkpoint spawn. I've tested that this works with the stock coop spawn. If any bugs are found let me know.
This is made to be dropped right between two chambers.
The default door state is closed/locked. You can use a simple logic_auto to open the entrance or exit(debug), or use a relay after a puzzle.

Included files:
Demo .bsp and .vmf
instances-
airlock entrance door
airlock exit door (requires entrance door)
entire check point (requires all other .vmf)

Feel free to edit the instances to fit your needs.

File Name: marlow coop airlock demo.zip
File Size: 943.15 KiB
Click here to download Marlow's Coop Airlock Spawn Instance example

Words cannot express how much I love you for this right now.

Lol, no problem. If you need a tester for your coop let me know. Steam ID:Sirmarlow2000

This should be an instance and not a "prefab".

Edited the title. I really do hope this gets some exposure, if only to promote the use of it's mechanic.

I were looking for this so much, going to be useful.

E: In example map that entry door opens properly, but I can't get it working on my map :S

E2: Got it working, had to add delay to logic_auto

MrLate wrote:
E: In example map that entry door opens properly, but I can't get it working on my map :S

E2: Got it working, had to add delay to logic_auto

Yes, as I said in the OP, the default state is closed. This is done because the entrance and exit doors are the same instance. They actually start open and are automatically closed. I should really remake them to start closed.

Glad to see you are using them.