Sircular
If memory serves me correctly, the maximum weight for a Renntec sports rack is around 11kg. It's not really designed for carrying a top box, more of a place to put a few bits n bobs I think.
Having said that, I created my own luggage system using the Renntec sports rack as the base several years ago, and it hasn't let me down over the years - other than the previous Renntec rack losing one of the fixing plates due to my inadequacy as an engineer
I frequently use a Renntec rack with a Givi base plate fixed to it using a couple of brackets to secure it firmly to the Renntec. Then I add the 45L Givi top box, and it's as secure as anything else I've had. I call it the Giv-n-Tec
I did post details on here several years ago, but the forum has been remanufactured a few times since then and lots of useful (and useless) information has been lost.
I can also use the genuine Honda luggage system with this setup too to give me the pannier and topbox option when required - whilst also keeping the rear
rail on the bike in case you want to remove the luggage system while you're just blasting around
I've had the Givi Wingrack and also the SW-Motek system, but for my money the simplicity of the Giv-n-Tec and the versatility of using it either with or without the Honda luggage system is the way to go.
If you want a photo of the Giv-n-Tec, let me know and I'll take one for you as it's still on the bike following my week away last week