Towing speeds in France

Having just driven (without the van) from Calais to The Jura region of Franc via  the A26 A5 A31 and A 39, all fast motorway, I noticed many caravans being towed at speeds in excess of 110kph. (70mph)I know higher speeds are allowed and road conditions and lack of traffic allow this but is it safe mechanically to tow at these speeds. Many of these vans were foreign, Fendt, Hobby and Hymer. What do other foreign touring caravaners think of this.