The maintenance manual or the owners manual do not specify the step by step instructions to change the coolant (i.e. what parts have to be taken off). But looking at the pictures in the manuals it appears as though you have to remove the lower left skirt in order to get to the drain plug. Is that correct?

The picture on p. 6-5 in the service manual shows the drain plug with the lower left skirt removed. You can access the drain plug without removing the skirt. You just need to lie on the floor and look up using a work light to see it.

Make sure you bleed any air out of the system using the procedure at the top of p. 6-6. The step-by-step instructions on p. 6-5 and 6-6 are very complete. Maybe you just didn't see them?