I just finished installing fridge fans. I did a lot of reading up on them and believe them to be one of the best and cost-effective upgrades to an RV. I ordered the dual fans from ebay, and overall I am impressed with the product. I have a 2014 with the Norcold N611 fridge, so if you have that same model you will need to run your power line out the drain tube and tap into a constant 12VDC source (easy to find on the back of the power board) because when the door closes, the light shuts off and there is no current supplied to that contact point like some of the older ones or Dometics.
I had a pretty good understanding of what needed to be done before I got into it (thanks to this site) but I also emailed Richard (the supplier) requesting detailed installation instructions, and they were sent to me just as I received the parcel. Installation took about 20 minutes taking my time, and I had all the parts (wire, fuse, fuse holder) on hand before I started. I used a 3 foot length of 20 gauge wire, a 500mA fuse (the fans together draw ~150mA) and an in-line holder. I shrink wrapped all the electrical connections after trimming excess wire lengths.
I'm quite glad I did this mod and had to run the wire down the drain tube because I found that there was a black stopper plug in the end of my drain tube! Anyone else find that on theirs? If you haven't looked I would highly recommend you go check to make sure your fridge can actually drain.
I also bought a fridge thermometer to monitor my temps, and will report back after our trip as to what kind of temps were achieved on which setting. I'm thinking number 3 or 4 will work.
Anyways, all in all, any mod you can do to your unit for under 20 dollars is worth it, and this one definitely is a good one. You can't go wrong buying that dual fan set-up for $14 on ebay - he will make sure you are satisfied and will answer your questions.