The Natural Explorer class feature is sort of vague about what skill checks count
When you make an Intelligence or Wisdom check related to your favored terrain, your proficiency bonus is doubled if you are using a skill that you’re proficient in.
I emphasized related to, because it doesn’t say "while in," so I’m wondering whether keeping watch in your favored terrain counts as related to your favored terrain. This could represent something like being more familiar with what’s naturally around, and so you have an easier time spotting what shouldn’t be — i.e. the approaching enemy.
Does it apply?