give the sills a good clean and wipedown with panel wipe (washingup liquid + water at a push) to get rid of any grease/wax before you stick the skirts on.
the cheesewire is for when you want to take them off again, its like serrated wire with a handle at each end that bodyworkers use to remove trim, then the thinners would get rid of any residue from the bonding agent that's left.