I have a 2006 Tacoma Access Cab and plan on mounting it in the cab behind the front seats, probably on drawer sliders.

Which size fridge is the most popular, best suited, and any hints for mounting?

Even though there are other great fridges out there, I will be buying an Engel and would like to hear specific feedback about their product line.

 

i would check out the expedition/camping folder:
https://www.yotatech.com/forums/f172/
might even check Corey's sig, i thought I saw a write up on fridges that he did.
another good source of info is expedition portal...
http://www.expeditionportal.com/

good luck, a fridge would be cool