Put those items crosswise on your seat and the little plastic thingy behind the seat.
Larger tent, sleeping bag, folding camp chair. Placed in tee pee config on passgenger seat and held firmly in place using 1" nylon webbing (one strap on each side). I have not tried Rok but have used the cheapie adjustable spring loaded steel buckles on the webbing and it works great.
Thermarest on little plastic rack behind held in place by old fashioned rubber bungees. You can adjust length of bungee by tying knot/s in it, or you can buy the bungee with multiple hole locations. I used the flip out latches on rear to hook one end of bungee and hooked other end on the grab handle.
Lastly, I threw on a few extra adjustable fabric type bungees for holding misc items like hat, water bottle, etc, on top of the teepee setup.