If you don't want to make doors by hand, you can use the pre-made doors available in
ABS's resource pack (if you haven't downloaded it already). To get to them, select the entity tool, choose "ABS TF2 - Doors" from this menu, and then choose the type of door you want from the "Objects" menu underneath.
Then you can pick them apart to see how they work. Don't forget that you'll have to add the respawnroomvisualizers on your own.