HeavyDuty CurtainSider - UL/HD sliding roof. Sliding roof for high demands. The new Curtain Sider UL/HD tops have been especially developed for high demands. The “HD” means “Heavy Duty”, and not for nothing! The hybrid construction reinforced with steel significantly widens the field of application of the modern Curtain Sider and shows once again why Edscha Trailer Systems is a synonym for sliding roofs.