Finished! That was fun, and there was some clever use of Tileset 7 too.
Tileset 7? Tell me more.
Tileset 7 can only be used via external editing. Technically, every invalid tileset behaves like 7.
Walls are solid cyan, backing is solid green. Spikes are Space Station style, and always face up. Background is Space Station style too. Interestingly, if the room was originally, say, Lab tileset, then the spikes and walls that are Lab-style will remain, and you can place Tileset 7 objects in addition to them.