I've kinda spammed this image in a couple places before, but this is a design that I've tried in past tests that has worked very well. I like to call it Zombie Auschwitz. What possible improvements could be made to it, if not scrapped entirely and another better one is found? I found this completely by chance in an attempt to contain zombies on Big Red and it worked spectacularly to the point that some of the only zombies remaining on the map that weren't gibbed from CAS and C-4 were dead in my containment.

My main thought process behind this was the use of girders. However, apop has said that zombies CAN damage girders with their swings now so this not a longterm defense unless you have a lot of metal to keep replacing the girders and a lot of flamer fuel to keep the pyre burning whenever they rise again, and too many will make containment completely impossible without constant fire.
The way this is intended to be used is to toss a zombie inside by crowbarring up one of the girders, putting a burst of flame on the corpse pile to prevent any from reviving and attacking you right as you open it, then moving the corpse onto the Z icon, and wrenching it back down where it used to be. If they revive inside, have a flamethrower burn the tile the corpses are on through the girders (due to flames passing through them) and this will kill them rapidly. For best results, take the flamethrower yourself as an engineer so you don't have to rely on anybody else to use one.