PID Tuning/Autotune

[BrianC]

I have never used a PID loop before but need to for a project. We have a reservoir tank with oil in it. When motors are running it will heat the oil from room temperature (70° F).  Once the temperature starts to rise, I need to activate our cooling system and proportionally control a valve to maintain the temperature at ~95°F. 

Every example I have seen uses the autotune, but i am not sure how to allow our system to run the autotune to get the correct values.  Also, the reservoir will respond very slowly to the changes, so I need to sample time to be 30 seconds to 1 minute between adjustments minimum. 

Is trying to run the autotune to get all the correct values the best thing to do in my situation, or should I try and manually enter values until I am able to reliably control the temperature? Is there any guidance on figuring out what values to enter for a manual tune?

Any help is appreciated.