After several trials with invisible blockers I successfully made it so the defenders cannot leave their bunkers. They could not open the bunker doors originally however once they were opened they could leave and it broke the game as it became a lot harder to kill them. I tried and tested team blockers with game labels, they worked for Team Slayer but blocked the infected(Attackers) and defenders. Therefor I oped for a slight inclined invisible blocker at the base of the door that the infected(attackers) can walk over and jump back over, but the defenders cannot jump over and leave the bunker as they only have 10% jump.

-All in all defenders cannot leave the bunkers, as I previously intended.
-Updated gametype as settings did not originally save