Had the same problem with my 18" Infinity QX56 I had to flare the bedsides out quite a bit to get these things to tuck, and even then it was still close! Just be carefull, and make sure you clear the rim lifted and dropped!
Here is a link to the Mini Truckin tech article on how to flare b-series bedsides w/o screwing them up!
http://www.minitruckinweb.com/tech/body/0309mt_fender_flare_tech_how_to/
Good luck!
Devon