I’m fairly sure that “boardable” means you can walk over it without penalty. Aisles, for instance, are “boardable”, as are cargo spaces. Doors aren’t, hatches are. Door can have a curtain added, hatches can’t (but add an aisle curtain, and it still works, just takes more resources/effort).
Flaming eyes (which are often near portals) gaze at you, and that can cause mutation (or perhaps radiation, which causes mutation…). I haven’t really bothered with them much in a while, so that might have changed.
Also, stepping into a portal can give you teleglow (basically, sickness from teleporting - it eventually goes away), and I think one of the symptoms (you get random crap from time to time when you have it) is radiation or mutation (or both), but it’s been a while since I messed with that, too.
There are also random spots that are radioactive - damage in the middle of road for no reason, lots of smashed trees in the middle of the forest for no reason… they can be radioactive (not all that common, but I found one on my current playthrough on a recent experimental, so it’s still around).
Stable genetics doesn’t help you NOT mutate, it just helps you get nicer mutations when you DO mutate for any reason.
