A tow bar has a nose weight restriction and I think the Cali is about 100 kg but I'm sure somebody will correct me if wrong. So any device you put onto the tow bar, caravan or box with Thule 929, should not exceed the nose weight restriction. It often gets overlooked but the bike rack and bikes also need taking into account when considering how much weight you hang of the back of the vehicle. That combined weight effects not just the rear suspension but also the handling of the vehicle. Anybody who has towed and badly loaded trailer/caravan will tell you how scary that can be!
I'm not saying don't use one just be mindful of the weight being added.