RCM on frieght charges on goods sold

My query is we sell steel with GST invoice on ex-premises terms. Hence whatever freight charges/transportation applies on such goods, we include in sales invoice, at 18% GST, same as our goods GST rate. 

Whatever transportation charges we apply in sales invoice to customer, same are paid to transporter.

Question is do i need to pay RCM @ 5% on such transportation as i am already applying GST @ 18% on such charges in sales invoice to the customer?