So I finally decided to check out the new FEMA camps dotted around the map, and as luck would have it I got hit with acid rain just as I hit the camp. I ducked into a tent and figured that I’d just wait it out - but nope, acid rain and acid splatter all over the place.
The problem mainly lies in two issues:
A) The groundsheet tile doesn’t have the supports_roof attribute, which is the one the game checks for when determining if a tile’s an indoor or outdoor tile if I remember correctly.
B) The labs (concrete walls) use pavement for flooring tiles, which explains how weather effects are able to affect their interiors. Probably better to use metal walls and regular floors (which would further give the impression of this being some fast-deployable deal.