Fastcamo is your main gauge. You want to keep it or stay close to it for maximum effectiveness across the board. I really don't think its even close to 95%. If I had to guess I would say its around 70-80%.

Explorer does seem to suffer less from being in civilized areas. Again, not enough testing to say for sure, but seems like it.

Also, you could always sit in the little grove to the north of the Inn. If someone comes in, then go hang out. Good way to keep your wilderness time up if you need.

You planning on PK as this herald? That could be rough. I don't think your skills will suffer enough for an exploration type character to be hurt though. I imagine things like bearcharge, wilderness familiarity, and camo suffering from low wilderness time.

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It's really not that hard. Just pay attention to your fast camo and react accordingly.