In my opinion, it is best to place key items so that they are fairly accessible, which makes them easier to get but in turn makes them harder to camp. In CTF I often like to put the most important items like Full NRGs/Power Ups out where they are easily reachable, which can lead to people fighting over them but in turn makes it harder to camp there safely. I also have lesser items like +1 Carrots/Ammo containers in slightly more sheltered areas so you feel safer to go ahead and get them, although you get less of a bonus for doing so.

A good way to deal with camping if you think it really an issue is to try and punish those who attempt to camp. For example, let's take City of the Sn00zE. The Undergroud route at the bottom of the level is the safest route in the level to take, and contains a rather convienient Seeker PU. While yes, it is very easy to camp and is hard to approach someone camping there, it is a potential death trap for the camper as the only way out of the Underground is to take either two of the warps on the side walls, which your opponent could camp either of the targets and get an easy kill. It is possible to RF climb your way out of the manholes though if you possess the skill, but since there is no RF in the Underground you only have what you picked up earlier. Camping by the Full NRG can be countered as it is very vulnerable to Bouncer/EB fire. Camping any other item in the level simply isn't worth it.

One really sneaky tactic is to have something like a hidden crate that creates a suprise pit to catch out unsuspecting campers. (DnC is an example of this) Or, you could have an area which has a pit open up if a player camps there for too long. (Undulation is an example of this)