My DMAX is used normally for towing my toys and I usually trailer 200 - 300 miles a trip. What would be the suggested supplimental gauges and any suggestions on where to mount them. I have looked at the pillar style mounting options. The cubby hole in the roof console I would never use and wondering if that can be used for mounting.

A lot of folks have gone with oil temp, boost and exhaust gas temps (egt), and in fact, that's what I have. If I did it over again, I would drop the boost and put in a water temp gauge.

Yes, I know you already have a water temp gauge - so do I. In towing a 37 foot 5th wheel trailer in 106 degree temps though, I found out the factory gauge is not accurate. Reading some of the posts here, it is speculated this is done on purpose to keep us in the dark on how hot the engine can get. My water temp gauge showed 215 while my oil temp gauge had readings as high as slightly above 240. Experience has shown me that oil temps and water temps should be in close proximity.