I personally would not mount any thing extrat to slide. Might get a rack for on top of you truck. I have seen Kayaks on them pullling a fifth wheel (The Truck not the Kayaks)
I can see it now. "Honey, paddle faster, dig,dig!" I made a home made rack for our kayaks. Works good. For shorter trips I just put them in the back and over the tailgate. Strap them down with a rachet strap.
If it isn't too much trouble will you post some close up pics of how you built it?
It was very simple. Measure depth and width of your pockets and trim 2x4 to fit. Leave them long enough so that your kayaks or boat will clear top of cab. Measure pocket to pocket for length of your cross members. I used 2.5'' deck screws to fasten together and painted it. I run a couple rachet straps over the kayaks front and back and fasten to rings in truck bed.