This thread might help HERE
The wooden piece you need is found in with the bridge items if my memory is correct, that can be destroyed a bit, What platform are you making the Escape map on ?
I have a map half way finished on PS4 called Escape Your Fate 2 but I have taken a break from the game the last month.
Use the elephant wall it fully breaks when u explode it. There is also a tree in the nature objects if set right can block AI and your path as well and it fully breaks apart as well, try covering holes with items in them with a barrel they can be pushed over to reveal the item and use posters or blankets to hide holes in walls also cliff vines in the nature section. If u want spawn one enemy in the air a Molotov or a beheader or a hunter from each wave to make your enemies spawn or surround a few with wolves n they'll get eaten lol still forcing your enemies to spawn without you killing any one. And if u want to make a nonstop survival use a chalk board n face it out n cover a watchtower they work like a one way mirrow/wall