Since I did not see any wetness on the carpet in the trunk I figured that the coolant tank was not leaking. (I assumed that the carpet sat on the metal floor of the trunk.)
I did a little more digging and realized that there is a particle board sub-floor in the trunk. I removed the carpet and looked at that and saw that it was all swollen with- presumably- coolant.
See this picture of the particle board sub-floor that sits in the right hand (passenger) side of the trunk. It is swollen in many places.
The piece on the left is the left particle board sub-floor that sits in the left hand side of the trunk. Not swollen. The main particle board sub-floor (not shown) was not affected.
So, yes I guess my coolant tank is leaking.
I will not go ahead and replace it.
I am also going to change the oil and plugs to make sure the coolant isn't leaking from the engine block just to be sure.
Thank you for all your help.