Yes that is a very high probability for denting the skidplate on a rig built for harder offroad trails. The skid is thin, as you mentioned, and doesn't have much in the way of ribbing or bends for structural support. In our case, my daughter's XJ is a daily driver and I just never like having the gas tank exposed for ANY reason, one being it is easy for thieves to simply drill the plastic tank to steal the gas. The skid at least makes it a little harder to do that, and protects it somewhat from other impacts. For reference, on ours there is about a 1" gap between the skid and the tank, so it can bend upward some before contacting the tank.
