The 1/4" sliders will hold up pretty good. Lots of folks running them. Drop from several feet onto a rock and anything goes, however. Ultimately, its still only braced by the rockers and front and rear door posts...if they are solid to start with then all bets are off. The 1/4" stuff will hold up to slides, stumps, rocks and medium abuse. As mentioned, many folks use some sort of silicone sealer to mount them. Body panel adhesive would make a great PERMANENT sealer and bonding agent (coupled with some rivets).
I used some HD SS rivet-nuts imbedded into my Line-X-ed rockers to hold my skids. I can remove them if needed. I used some closed sell foam to the skid to help to tightly seal to the rocker...but the Line-X does a great job of protecting the rocker. HTH.