A big research building with a bunch of rooms and a timer (and alarms) for Caustic gas to fill the place up out of vents along the ground (?) except for some safe rooms (maybe a control room and/or a security room) with indestructible doors that automatically close when the gas comes. Caustics would be able to roam around freely during the gas phase.
This would incentivize people to congregate and fight over specific rooms, and if the gas comes and you get stuck outside a room you'll just have to try and heal through it. The threat of getting stuck in the research facility while the ring is encroaching on you is a real one, and players would have to plan for that.
Respawn would probably have to make there be some pretty good loot incentives inside the facility, otherwise players probably would largely avoid it. Would obviously be a really cool caustic playground, and you could even have lots of rooms with opening doors so caustic gets to use his gas traps to block them. I would implement plenty of exits, and I wouldn't make the building crazy big, I do think it should be bigger than any of the buildings currently on the map, though.