I was thinking about your typical party campsite the other day. We assume both as players and as GMs that a lot is happening during those hours camping that we do not normally play through. The fighters are practicing, repairing bits of armour, food is prepared and pots washed and so on.
It is easy for a typical PC to be ‘learning’ 15 to 20 skills each level and all of these will require a certain amount of practice time. I used to work in adult education and we would allocate about 20hrs for a student to grasp a basic skill. It is also generally bandied about that it takes 10,000 hours to master a skill.
I imagine some campsites get quite tense with the characters trying to learn academic skills getting really hacked off with the fighters shouting, grunting and clashing weapons all evening. Combat practice is really hard to do quietly. I was at a fencing competition on Friday and there you have steel weapons but cloth armour or polycarbonate breastplates. The sound of the combat carried maybe 300meters or more. Imagine steel weapons against iron bound shields and steel breast plates. The typical ‘off guard’ or off duty party could probably be heard half a mile away on a still evening and that is without the swearing when the character fumbles a smithing roll whilst hammering out dents in his armour.
If your party, as I often do when playing, says they are going to make camp away from the road so they are not obvious you are in reality talking a very long way if they are going to carry on the normal business of maintaining their skills and equipment. This doesn’t even take into account particularly keen ears of non-human races.
I think this is one of those things I have just taken for granted ever since I have been roleplaying back when I was 14 or so and that has just always been the way parties camp. In future I think unless other precautions are being taken you will be looking at an active zone nearly a mile in diameter when a full on PC party makes camp. No wonder orcs, trolls and goblins wander into camp so often!