I am thinking under the battery tray would be the best spot but lets see some pics of where you have it.

 

Why do you need an external transmission filter?

Do you mean a cooler?

 

mainly because it is allot easier to change, filters out smaller particles, and came with a boss for a trans temp gauge. I also have a auxiliary trans cooler. I don't want to grenade this trans.

 

The filter inside the tranny pan does a fine job of keeping metal out of the oil. You need to have the internal filter for the pump to suck up oil and anything that gets through that filter, will probably be too small for the external filter. Under extreme use, the internal filter should be replaced a minimum of ever 2 years. Under normal street use, 5 years is fine. An external filter would never get dirty. It's a waste of money.

You won't like a temp sensor in a cooler line. Temp sensors should be in the pan to tell you how much heat is in the oil after it's been used. If in the cooler line then it's either hot from going through the pump or too cold after going through the cooler.

The only way an external filter would be effective if it was installed between the oil pan and the pump which you can't do.