I know this will sound GHETTO but it has worked for three years on mine and I had WAY more weight on mine than you do for instance I had a 33 inch TSL spare on a wheel up there all the time then when we went camping I also had the tent a HUGE bag for clothes and whatever camping gear up there we needed... ALSO I drive kinda crazy and NEVER had an issue with it sliding... are you ready for this??? I used hose clamps to the factory roof rack cross bars
here is mine with lights

on this pic you can see the hose clamps at each corner of the rack

here is a view of it while I was building it


FULLY loaded for camping trip... notice how much the back is sagging... half that weight is on the rack


I am happy with mine over the years but lately I decided to build an EXO cage so I took mine off and I think im gonna use the rack to retro a go-kart for the kiddos to use while we are out wheelin