Hi, I have a 2012 Fiat 130 Ducato which has been converted into a motorhome/ motorcycle race truck, all professionally done but if I put one bike and all the kit in we are getting 3,640 kg, just under the maximum, is it possible to increase the load capability to 4000kg by adding an upgraded rear leaf spring to be able to carry another bike?? Plenty of space to do, Hope someone can help, also what would you need to do if its possible to upgrade with changes to the Data plate and log book, I have been in touch with the Conversion company and they said no upgrade was done when the conversion was carried out, Phil