Tough Touring can supply small flexing mounts to suit the installation of Roof top tents  that need to bridge across articulating vehicles tub/ canopy / trays . (Dual cab utes). 
We have a variety of sizes ranging from 40mm up. 
Please let us know the size required once you have your racks accuratly measured for height. 
We would reccomment that these mounts be used in conjunction with Tough Touring Over Cab Roof racks - as these provide ultimate strength / foundations for yoru rtt over the cab. 
These Mounts are a 'secondary' support only and should not be used for overall strength, just to prevent downward load forces when people are in the tent from bending the tent - (Tent sag). 
 
The Mounts will allow up to 30mm max flex distance - (15mm each way) and have excellent anti compression properties.