2003 Nissan Frontier Owner's Manual - Page 304

LTI0123 WTI0119 1 correct installation, 2 incorrect installation WARNING Do not install accessories over the gap between the front and rear side channels. Doing this could affect the rear structure in certain rear impacts, which could result in serious injury. CAUTION Properly secure all cargo with ropes or straps to prevent it from sliding or shifting. Use the channel end stoppers to help secure items in the channels from sliding off the end of the truck bed. Channel End Stoppers (if so equipped) The channel end stoppers should be used to help prevent accessories installed in the channels from sliding or shifting off the end of the truck bed. 9-20 Technical and consumer information