You will first need a multi-purpose base rack sytem that will mount to the 01 Mercedes Benz ML 320 roof rack siderails (the two bars that run parallel from the front to back of your roof top). The
Yakima Lowrider roof rack system will fit your side rails perfectly and is very quick to install. The Lowrider system includes four Lowrider Towers that clamp onto the siderails and also a pair of crossbars that connect to the four Lowrider Towers. You can then connect the cargo box for carrying your gear to the two crossbars.Remember that you will need to go with the 58" crossbars as this is the length necessary to span across the 2001 mercedes ml 320 rooftop.
So you should then go with either the
Yakima SkyBox Pro 16s roof box or the
Yakima SkyBox 16s roof box (both cargo boxes are the same except the SkyBox Pro series has a glossy finish and the SkyBox has a matte finish). The 16s is ideal for your needs as it has a good shape and cargo capacity for your guitar, clothing and other miscellaneous cargo gear. These roof boxes will also provide great protection and are also waterproof. They also include locks to lock your stuff inside the roof box.