It is just a static boolean property that you typically you would like to set during initialization so you could do it either in Application_Start or in an IInitializableModule.

Thanks Johan, It worked for me.
Regards
/K

What am i doing wrong:

I want to add the slash and also make the url lowercase..

this is my initialization module but url stays the same without slash and no lowercase: 

Am i doing something wrong?

[InitializableModule]
    [ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
    public class RoutingInitialization : IInitializableModule
    {
        public void Initialize(InitializationEngine context)
        {
            //Add initialization logic, this method is called once after CMS has been initialized
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            WebApiConfig.Register(GlobalConfiguration.Configuration);
            EPiServer.Web.Routing.ContentRoute.UseTrailingSlash = true;
            EPiServer.Web.UrlSegment.UseLowerCaseSegments = true; 
        }

        public void Preload(string[] parameters) { }

        public void Uninitialize(InitializationEngine context)
        {
            //Add uninitialization logic
        }
    }