For the zombie spawn in open areas I tried antiportals with varying results. The revision of HappyHour, not too good because when the patty spawns he's sometimes in the middle of the antiportal with freakish results for players watching xd.Safest to place big stones with antiportals in the middle of them and the zombies spawn behind. Make sure the antiportal thickness is greater than 16 units
For the zombie spawn in open areas I tried antiportals with varying results.