I have the Grenadier Rhino Rack Roof Bars and I'm looking at how to load my Mont Blanc cargo box onto it. Has anyone used U clamps to attach a roof box to the RR bars? I haven't seen them sold that wide! I only use the roof box 2-3 times per year so don't want it (or the cross bars) permanently mounted. If the cargo box can only be mounted with T bolts or T nuts, is there a packaged RR solution that I can buy? I'm based in the UK and struggling to find where i can buy it. Thanks, Warren